To place or remove a check mark from a menu item, use the WMENU-CHECK or WMENU-UNCHECK operation code. Follow this by the menu's handle and the ID of the item you want to modify.
For example, to place a check mark beside the menu item 10, use the following code:
CALL "W$MENU" USING WMENU-CHECK, MENU-HANDLE, 10
Placing check marks on top-level menu items has no effect.