How can i get my high notes back after I hit puberty? P.S. I'm a thirteen-year-old guy.?

You cannot reverse the growth of your vocal cords/voice box. Their growth can be delayed by neutering, but there are a few side effects.

Look into learning how to sing in Falsetto, which will basically take your voice up into the female Alto or Mezzo-soprano range- (depending on how high you're personally, able to sing, using this particular technique!) Some blokes even manage to get their Soprano range back again, using this particular technique, but this is somewhat rare though. I think ya might have to be happy with achieving either an Alto or a Mezzo-soprano voice. Come what may, I wish you all the luck in the world, old son. Peace and love. Be lucky, brother.

You canNOT get everything back after puberty, sorry. Puberty is inevitable!

By removing your testicles, however, that is not recommended.

Try and practice higher notes everyday?

What an utter load of nonsense and cra!!!!... advice from idiots. Number 1, you will not have Boy soprano Voice as you go through puberty but like all adult males you will learn to sing Falsetto, which means false voice in Italian and this is when you use cranial resonance or bone conducted sound to sing very high notes. A good voice coach will help you succeed with this, but you will sing high notes just with different palatal or cranial or nasal choice.

What you really mean is high voice because there are high notes in every vocal range. You will not get your high voice back unless you castrate yourself.

There's a way....but it's a hard way and once you take it, there's no turning back. I wonder, are you committed enough?

You will have to be neutered.

Work hard, maybe?