Had to switch to a new email address recently, and managed to change it here on the forum …
But not at Bambu Lab itself, nowhere a normal possibility to do so, as on other websites.
Even went through the trouble contacting them directly.
Not possible 
and on my question why and how in this world they think changing an email address is never happening to their customers, there was no answer, other then … So sorry 
I don’t expect a quick solution here, but it is a very inconvenient situation…
It is part of their ‘security’ measures…
A few other websites do similar 
Officially it is meant to prevent account theft/abuse by making sure the original user won’t get locked out by a hacker.
Sad reality is that these measures simply don’t work as advertised and so only made a mock out of users like yourself.
Some websites/forums allow you to change the Email address using a ‘trusted device with their app running on it’, like some banks.
But in most cases the only way seems to be to go through their support, verify your credentials and once cleared the support can put in a new Email address.
Bambu enforces all this bogus based on providing a better service and experience that is much safer but if you ask me then all it did so far was to create hassles we should not have…
Appreciate your advice … But I went already through all of that, even their support employee couldn’t help me with this …
And even changing my email address at my bank wassent impossible, took just a few extra security layers but still possible.
Sigh … In 2 months I lose access to my old address and totally not happy with Bambu Lab on how they manage this for their customers …
If the support can’t help it only means they are badly trained and/or won’t have the required access - spreadsheet artists…
Ask yourself how bad this is for you and how easy it could be fixed - then you know how little Bambu cares about their customers 
Making money counts, providing things that work out of the box as advertised, happy customers not so much…