Checking for duplicates in a column

Very new to Monday for our nonprofit so not up to speed with all the technical terms. Apologies!

We have an event coming up and I’m trying to use Monday as an active rosta for the event tat we can change on the fly as the event goes on.

Item Groups are time slots and each item is a specific task. There is an ‘Assigned’ dropdown columns with people’s names in (it’s not a ‘people’ column as the people being assigned don’t need to see it, just myself and another colleague).

I want to make sure that I don’t assign a person twice in the same time slot. Is there a way I can either a) make sure they don’t appear in the drop down once they’ve assigned or b) have a second column that warns me if they’ve already been assigned to a task in that time slot?

TIA.

Hey there! So sorry for the long delay responding on this! Hopefully, these questions were figured out by now but if not, please shoot us an email at support@monday.com so we can get this resolved efficiently together!