I've tryed using ./ncc_att_hwid -f openwrt-18.06.4-ramips-mt7620-dir-810l-squashfs-sysupgrade.bin -m "DIR-810L" -H "A1" -r "WW" -c "1.0" -F "1.02b22" -a. a bit modified then given on guide but that's because of different version of hardware (A1) and software (18.06.4)
I get -bash: ./ncc_att_hwid: cannot execute binary file: Exec format error and ./ncc_att_hwid: 1: ./ncc_att_hwid: Syntax error: "(" unexpected depending on "user" (Syntax one is with sudo and other one is without).