Not able to change Why are you changing the salary for [TM name]? into mandatory field

Summary:

Not able to change Why are you changing the salary for [TM name]? into mandatory field under Change salary

Content (please ensure you mask any confidential information):

Hello Oracle Community,

Hope all are doing great.

Our requirement is to make "Why are you changing the salary for [TM name]?" mandatory under Change Salary Page.

Navigation:

My Client Groups > Quick Actions - Show More >Change Salary > Search for TM > Select +Add > Why are you changing the salary for [TM name]?

After checking HCM Design Studio I didn't find any area from where I can make above field mandatory.

Could you please help me with the feasible solution for this requirement.