PowerShell script to replace a user Identity

I'm having SharePoint 2016 On-premise environment, now we have a requirement as follows.

we have nearly 100 SharePoint Groups, where we had already have many user's identity added as DOMAIN\username ,now we want to add their full Email ID [email protected] to connect the site with Azure AD. In other words, in each group we need to take a list of existing user IDs (DOMAIN\username)and add a new Identity( [email protected] )for each user in the same group.

Initially we started adding the IDs manually, but its time taking process.

can anyone please suggest a power shell script to complete this activity easily.