How to make Expiration Date in Offer Letter section required

Content

I've been searching through the Actions in HCM Studio to locate the section that includes Expiration Date in Offer Letter section, but I cannot seem to locate this. My goal is to make the Expiration Date in Offer Letter section required. I had recently posted this question prior and received suggestion to make this change using Page Composer. I'd like to resort Page Composer as a last resort and would prefer to make this change using HCM Studio. 

Can you advise which Action I should use to make this change for Expiration Date field?

Thank you.

Version

20D