Restriction of reassign option in Vacation rule setup to "relief officer" (Absence Mgmt)

Dear team,

Please how do I restrict the reassign option in vacation rule form to pick the relief officer a user selects during "absence management".(leave creation).

Here's my scenario:

I want a situation where the reassign option of my vacation rule selects my relief officer (during my absence creation) automatically. This is to enforce security that I do not choose just anyone as my reassign officer but my relief officer.

See attached my  vacation rule form and absence form.

In summary I want a tie between my "relieving officer" in absence management and my "reassign option" on vacation rule setup