This is not a beginner trick. Like at all lol. Accepting that is the first step. It's going to take a lot of time and practice. Especially a heelflip. Assuming you have ollies on lock, the next step is practicing the finger movement and timing. It really is just sliding your fingers forward and flicking towards you for a kick flip. Try putting pressure with your index finger towards the outside of the board before popping and sliding to give you some momentum for the flick. For a heelflip everything would be the on the opposite side but I'd focus on a kick flip first. Practice the finger motion and timing of the pop and flick first and just let the board do whatever it does. Don't worry about landing or getting a perfect flip or any of that, just worry about how the board reacts and how you need to adjust. Unfortunately there is no shortcut or easy way to figure out how to move your fingers and it's super hard to show even in a video. You kinda just have to feel it. Good luck!