How to disable/enable a access to ERP SaaS environment for all users except administrator

Summary:

We got a instance after P2T refresh. Since the password from prod remains same some of the user have the access for test instance. We want to remove the access of all the users so that no one can access the instance and perform any transactions. We have around 40-50 users. It is very difficult to disable the users manually. Also we do not have HCM so we cannot run the user.dat to deactivate the accounts.

Once we are done with all the post clone activities , we need to restore the access as well.

Please provide your suggestions how to achieve it in an efficient manner.