Identify Microsoft 365 cutover steps

I have migrated all of the mailboxes. I am looking for consultation in figuring out the next steps. I just started working on smtp relay. I need to understand how to do the cutover now. This specific project is for consultation where you can give me steps. We can open another project for a working call since I cannot make changes to production without a change control process. Thank you.

Please ask questions if you have any. Thank you