lol no, we don't buy things here, we pirate it all because we can!

here's tasha's cauldron of everything book
see character options - customizing your origin i think it's about redistributing race specific ability score increases and proficiencies so it fits your class even if your race originally doesnt. for example cats tabaxi has ability increse 2 in dex and 1 in wisdom
also proficiency stealth which is useless for berserker, better put that in strenght increase 2, dex increase 1 and swap stealth skill for athlethics or something.

see if you can figure out which changes are allowed.