Remove "Reassign Activity" permission from "Hiring Managers" group in Onboarding.

In the Onboarding, we want to remove the "Reassign Activity" permission for the users belongs to "Hiring Managers" group.

We tried unchecking the option "Reassign Activity" for the Hiring Managers group. But after that also hiring manager is able to reassign the activity.(The tested user belongs to only "Hiring Managers" group).

Can anyone help on this ?