MFA skip and re-enable

Hi Team,

We have custom applictions using IDCS as IDP. We have changed the Enrollment option from required to optional by following the navigation -> Domain->User Category Based SignOn Policy-> Default User Category Based SignOn Rule->Enrollment->Optional. Now, When we access the custom application->we got the MFA option and skip option. We clicked on skip option and accessed other sub applications, no where it asked for MFA. This is fine.

But if the user want to enable MFA in future, how can the user do it. For this purpose, We tried changing the Enrollment option back to required from optional in the domain. Tried to access the custom application, it is not prompting to enable MFA. In this case, how can user enable MFA if he want it.