Basically what the title says, I have some large tsv file (approx. 20k lines) and I want to delete the rest of the files after a specific column matches a string a second time (including said line)

Delete all the lines including and after nth occurance of pattern
awk '{print $0} $1=="yourstring"{if(++found==2)exit}' test.tsv

Where $1 is the "specific column" and yourstring is the string you are searching for.
This prints each line and then checks for the occurrence of yourstring in the first column. If it finds it, it tests a variable found which we increment, to see if it hits 2. If so awk exits.
Edit: If instead you want to delete the second occurrence (as well as everything after), flipping the two blocks around will accomplish this:
 awk ' $1=="yourstring"{if(++found==2)exit}{print $0}' test.tsv

