Move account to another forest

Dear.
We have two forests with a forest trust between them. Today, our users are in Forest A, their Exchange 2013 mailbox too. We want to move the user accounts to Forest B while their mailbox remains in forest A.The accounts are synced between both forests.

Are there command line, PowerShell command we can use to automate this? If so, how.
Does someone has a link to a good article or document describing this procedure?

Thanks in advance.
Regards.