This is a standard JAMS functionality for Tenant Administrators, i.e. accounts having the Superuser role.
Such accounts can impersonate any registered user of the tenant (author, reviewer, editor or editorial board member) simply by looking up the account to impersonate in the Switch to another user lookup bar in the Super User menu.
The tenant admin can then make any operation in the system on behalf of the impersonated user. At any point in time, the admin can switch back to her/his account and stop the account impersonation.
This functionality is particularly handy for a Journal Editor or Managing Editor to unblock situations where other users are stuck and can not proceed for some reason.