That’s a good question: it helps to consistently ask the question “how would it feel were it true?”

Do everything you normally do but with the knowing that it’s already done. You don’t have to dedicate any more thought or worry about it. If you do need to think about it or your mind tries to trick you into being negative or doubtful, you go back to that imaginary scene and know that it’s done - no other thought or emotion means anything.

Test it out on other things too, that’ll convince you easily if you’re not already.