browser hijacked (?)

when i go to safari, my homepage is perfectly fine and normal. but when i search something up, it sends me to a yahoo search engine. it annoys me so much. ive searched up solutions on my phone but they're not helping. ive already checked my preferences, everything was fine. i checked my safari extensions but i wasnt using any, neither did i have/download extensions. i think the reason why i got browser hijacked is because i search up how to download apps/applications/programs (such as adobe premiere pro, after effects) for free (because im broke) on youtube and i download the links the channels give. they worked, but i started to realize that my search engine kept sending me to a yahoo search one. but my homepage was normal. a few days ago, i decided to delete all the applications that i didnt recognize or the ones that i downloaded from the links. there were NUMEROUS unrecognizable files that were in my finder. but my search engine still sends me to the yahoo search thing. it irritates me so much, i want to get rid of it. what do i do??