Migrating of users from OpenAI instance to another instance using PowerShell?

We have OpenAI instance of 16 in 3 different subscription and having 13k+users are in the all the 16 subscriptions.

My client decided to move all the 13+ open AI instances into 4 instances.. i.e. 13k/4 = 3k+ users into each instance. the distribution of the users migration has to move into 2 instances of (Subscription1 ) & other 2 instances of (subscription 2).

This entire process needs to do in Azure PowerShell.

Can some one guide me how to achieve this in the Azure PowerShell?

This entire script will be replaced in Automation accounts.