debian – root password not accepted

I am setting up a VPS server running Debian 10 and Apache 2,4

I must have done something wrong when I did a modification in the passwd file because now I am not able to log in as root.
I have two users. root and petter
User petter is working but has no adinistrator rights.
So what do I do now to recover my settings ? I have copied the passwd file on my notepad but cannot alter the file from my ‘petter’ user.

I a using PuTTY to connect to the VPS.

Please help me :-]

Petter