How the hell do i stop overthinking / worrying too much about

For me depression did the trick. I realized that in the end nothing that we do matters because we all die. People think "when we retire then we will live our lives" but when you actually get there you realize that you spend your whole life doing shit you didn't want to do and worrying about shit that didn't matter at all. When you realize all this then you just kinda start doing things you want to do and live day by day.

Set goals and work hard to achieve them. Put aside time to yourself and allow yourself to shut your brain off for a moment knowing you've done everything you could to progress your life.

Putting aside time for other activities is important. If you work too hard and too often, you'll burn out. If you don't work enough you'll get caught up in worrying about your life.

Practice being present in the momment instead of in the past (memories) or future (expectations).

How?..
For once, you can meditate. That's pretty much being in the present in whatever mod it comes. I won't lecture you on it though, since you can find MANY kinds of meditation online.

Read books that help you be present. One of them, for me, is The Power of Now by Eckhart Tolle, and The Way of the Superior Man by David Deida.
*there's one for women too, Dear Lover.

Whenever you find yourself worring too much, try to be out of your mind. How? Action. Do something, write, sing, jog, work... That puts the emotion in motion, depleting it's strength.

I have to point out that being present, like anything else, requires practice. You've been your whole life practicing not to be in the present moment, so time is needed to achieve helpful results.