Switching users to another domain (MoH Madagascar)

Hello dev team,
Currently we are in the process of transferring our environment in "commcarehq.org" to a local instance, so we have acquired a domain name for our local instance "sic.snis-sante.mg", and we want to gradually switch users to this domain name before the final migration to the local instance once the latter is ready

to do so we are following this documentation :

In this context, the "old environment" will therefore be "commcarehq.org"
The first step has already been done, we have already pointed the new domain to the old environment

And we ask for your help for the rest of the steps (2 to 4) since these must be done on the old environment, in our case it is "commcarehq.org"

Thank you so much for your help