Accesso impossibile

I installed a NextCloud server on raspberry several months ago and used it as a network disk accessing it from other LAN computers.
A few days ago when I turn on a macbook pro a window appears with the following written in italian language:


As you can see, the password for the user “ADMIN” is requested and the admin account @ ook pro shows me a window with the following written in Italian
As you can see, I am asked for the password for the user “admin” and the account admin@

Since I don’t remember it, I tried to reset it by clicking on the appropriate link in the window, a larger window appears that asks me for my username or email, but when I type it I am told that it is impossible to send the email for the password reset and I am asked to check that the username is correct.

I don’t think I have communicated to the installation a different email, but in any case there is no possibility to be able to enter as an admin on the server if you no longer have the password and do not even remember the username?

I add, however, that in the meantime I can easily see all the files that are present on the NextCloud server and that if it were not for those requests that are made to me (which in the past never came) I would say that it works as always.