there are plenty of threads on this forum regarding this topic. Depends on which gopros you own. The GP 5/6/7 does not allow you to connect mic directly, so its a bit more expensive to sort out.
But your best bet is to plug in a good wired mic to your smartphone, record it there and then just sync the audio in postproces, easiest and cheapest solution
Gopro Hero 7 Black
Gopro Hero 3 Black
Previously: Gopro Hero 5 Black / Gopro Hero 3+ Silver / Feiyu G5 gimbal / Xiaomi Mijia 4k