If a customer accidentally entered an incorrect email address at checkout or if they no longer have access to their previous address, you can change their email in Monto so they can login with a new email address.
This requires Monto's (currently free beta) CRM App.
Go to the Monto CRM app
Find the customer you want to change
Click into their profile and click "Edit" by their email address
Change the email address as you want it to be and click save
Now when the customer goes to your customer portal login subdomain, they can use their new email address to login. The old login will no longer work.
Note: Changing the email address in the CRM app does not update it in Stripe. That must be done manually in Stripe. Also, changing a customer's physical address in the CRM app does not update it in past orders.