I'll save you a course

1) get tested for total testosterone, Vitamin D, and get your yearly complete blood count, metabolic blood testing as part of your physical at a minimum

2) if your metabolic or CBCs are messed up, that's your priority first. Fixing any issues there will help and it's more directly important to your overall health. Your doctor will assist you there.

3) if your vitamin D is avg or less, take supplemental vitamin D and go outside more, it has a direct effect on testosterone. You can take it over the counter or get a cheap prescription from your primary. It is often low in western men and is considered critically important.

4) if your total testosterone is over 650, you don't need to do anything drastic, just keep exercising, eat healthy, keep your body fat reasonably low (edit: avgs 18-24: 692, 25-29: 669, 30-34: 621, 35-44: 597, 45-60: 550)

5) if it's below 500, ask your male urologist for/about Clomid. It tells your balls to turn your testosterone production back on, has no major side effects and unlike TRT makes your balls bigger and more fertile. Do this only if extremely low or if you've already fixed your diet and weight and it's still low (some guys bodies suck at turning production back on). (Edit: Unlike TRT it can't push you over your genetic limit and works on most people but not everyone.)

6) if you're between 500-650, look in the mirror. You likely already know in your heart where you're lacking. Diet, muscle mass, cardio, all need to be considered good or better.

7) in regards to gym: Bench, Squat, Deadlift. Biggest muscle groups worked means the most possible testosterone gains. Don't over work, 3-4x a week is fine.

8) in regards to diet: Eat less sugar, more fiber, more protein, more leafy vegetables, more olive oil, less cheap vegetable oil, more black tea (unsweetened)

9) if you drink, stop or at least drink very little. Liquor is better than beer since beer increases estrogen

10) smoking (both weed and tobacco) has negative testosterone effects. Not sure about vaping

11) for cardio, you don't need to be preparing for a marathon, maybe just aim for 1.5mi 3x a week under 12.5min. Going too heavy on cardio can lower T. I picked that because that's the minimum standard for the US Air Force and should be a good balance between cardio health, muscle development and hormonal results. If you have an Apple Watch, check your VO Max % too.

12) Aim for 10-15% body fat as a goal, but under 17% at a minimum. Below 10% can sometimes have weird effects on hormones, and anything over 17% is probably going to start tanking your numbers.

13) Take Magnesium and Zinc

14) Nearly all directly marketed "testosterone supplements" are snake oil. the only ones besides typical vitamins that could be considered useful are "DIM" which is a VERY well proven estrogen reducer and "D-Aspartic Acid" which is a tasteless supplement you can get in a powder form that will boost your testosterone if it's low. (It won't do much if you have decent levels). (Examine.com has research articles on both of these)

15) TRT should be a last resort. While it undoubtedly works, Unlike Clomid which I mentioned earlier, TRT makes your balls turn your natural production off, so you end up with tiny unusable balls with low sperm counts and has other major side effects as well.

16) There are actually good libido boosters. Horny Goat Weed, Maca, Fenugreek, Longjack, Ginko balboa all do work for libido (I personally like HGW and Maca). You can literally buy a month's supply for the equiv of 3 gas station pills on Amazon. None of these boost testosterone but are fun. I used to get these from time to time

"Ok but I still would like a book or more info"

That's fine, I got you.

First up is a set of long well written articles on the "Art of Manliness" blog detailing his transformation on boosting his testosterone naturally. Originally written in 2013 he did an update set of articles in 2020. He's not trying to sell you weird products, it's an honest to god guide based on his own experience

AoM blog

As for actual books, Google 'libgen' and on that site search "testosterone". You'll find plenty of actual pdf books and research docs. Some are sketchy and low quality, others are very good. I'd pop over to Amazon and Google titles and find one well reviewed.

As for a course, most are going to be kinda scammy, so I'd honestly head over to YouTube. Search for testosterone foods, workout plans, foods that lower estrogen, etc. if they're trying to hock tons of products take everything they're saying with a grain of salt, or find a different channel. The best often don't have to shill every waking moment. While not the best "Gravity Transformation" is a pretty good channel.

Edit: "Naturally Triple Your Testosterone: A Guide to Hacking Your Hormones and Becoming Superhuman by Peter Paulson" is on libgen