Dear Sudhakar,
As discussed the POS (normal POS mode) return (F7) privilege option can be removed for a user by disabling '"Allow Return" option in POS user role setup.Please find below path.
Module:
HO-->Retail management-->Security-->Configure-->Role-->Access rights(tab)-->Normal POS-->Available options(section)-->Allow return
POS-->Adminsitrator--> Security-->Role-->Access rights(tab)-->Normal POS-->Available options(section)-->Allow return
Note: Enabling/Disabling "Allow Return" option in normal POS mode will also enable or disable other return options available in normal POS mode window. (such as (F5)Return mode is OFF/ON).