you should not be too regretful, take advantage of the existing situation, when the cheap price always try to buy coin and sell when the price is green and when it is getting the benefits and better you control your patience.
You can handle crypto regret by not repeating the mistakes you made in past. Keep looking at the market condition and start modifying your plan to stay safe. Keep the investment long term and stay optimistic by which I mean to say do not panic. You will be able to kill the crypto regret when you earn again big with your mental capabilities and market knowledge by playing the same crypto game.
Learning from your mistakes, this is a better way to not to regret next time but the foremost is to make your mind easy with loss and profit. Dont be just over reactor after a profit and never lose your heart to quit trading once you get loss. This must be practiced again and again and your heart must be so strong to even make the things better. You are a strong man and never lose hope then.
To be honest, it is never that easy to bear losses when you have tried hard. But there is nothing more useful than accepting them as soon as you can and try to figure out where all went wrong. Learn from your mistakes and let not them put you in loss again ever. I am of view that every mistake has some motivation and lesson for you, you need to figure it out. You can either cry over mistake or make a motivation.