I have to change my email address with moparts

How can I change my email address with Moparts website without setting up my already email address

Upper right click on your user name. Then click on edit. Change what you need and save.

Don't bother , most big mail servers block all the mail from moparts

Have you considered fixing this? SPF records, DMIK, and DEMARC proves the sending domain is legit and it's not that hard to do...