You can also access the scan list programming via a long-press of a button mapped to SCAN, or by setting a switch to Scan List Prgm. If you have a display radio, the easiest way is to add a soft key SCNL item, as
@K2NEC noted.
You also need to set the Non-Priority Members field to Operator Select in each appropriate scan list, otherwise you won't be able to edit the list.