To operate on a check menuitem object and based on your requirement, you can use any of these functions
click - Click on the check menu item
menucheck - Tick the menu item
menuuncheck - Un tick the menu item
selectmenuitem - Select the menu item
verifymenucheck - Verify whether the check menu item is ticked
verifymenuuncheck - Verify whether the check menu item is unticked
Linux Desktop Testing Project