I signed up with an account linked to my Google account.
I now want to move it so I can log in with my e-mail adress and a password.

Of course I don't want to lose all of my data.
Does anybody have any idea how to do it?

I tried to fill in my e-mail address, but I can't since I need to enter my current password.
Which I of course don't have because I sign in with Google.