The traditional advice when it comes to dating is:
"Just be Confident Bro!"
However, you can't fake confidence. Confidence comes through experience. Failing again, and again, and again, and learning from such mistakes gives you confidence, because you now know how to handle the situation. Can you do it as a short term solution? Sure, but that shouldn't be your end goal.
What if I asked you to fly a full 747 jet, and you've never flown before, do you think you would be confident? Probably not.
That's why I argue, that in order for you to gain full confidence in dating or life, you need to go out into the real world and fail. Again, and again and again.
Remember "The worst objection is the objection you don't know how to handle". Maybe your starting from a blank slate and you don't know how to deal with 99.9% of objections. That's totally cool, everyone starts somewhere.
Or maybe your a seasoned pro out there, but you just get tripped up by those curveballs she throws at you.
I know in my dating life, I've done things and said things that make me cringe and just want to shake my old self saying "why would you say/do such a thing????"
Embrace such mistakes, and learn from it. Next time you come around, your arsenal is just a little bit better, and hopefully she throws you a curveball, so you can fail and know how to deal with that scenario.
When you have that arsenal of knowledge knowing how to deal with any situation, THAT'S confidence.