Help! With A Checkbox Problem

hey all, i have a supplier table (Supplier), that has a yes/no check box column field depending if they are active or not. About 200 suppliers in all, many of which not active.

I want to be able to automatically set the active field to True within the supplier table depending on the condition that records exist in my delivery schedule table (Schedule)

SO for instance if a supplier name "Power" exist in my delivery schedule, then i want supplier "Power" in the supplier table to be checked i.e True. I guess some form of dlookup is needed here, but not im not sure where to start. Any help appreciated!