How can we restrict values of a DFF created on Positions upon selecting a particular location

Hi all,

We have a requirement where we need to restrict the values of a custom DFF that we created on Positions page based on location. For ex, while creating a position, when we select a location, based on the location we select, the values in the DFF should be restricted to that particular location. User should not be able to see all the values in the DFF. Please help us.