Fixing an ssh and sftp lock

General problem: I blocked myself from controlling my Ubuntu operating system through sftp and ssh.

What caused the problem: A genius movement blindly following this tutorial:…ess-on-ubuntu/
What I was trying to do exactly has little relevance, but in case you want to know (although I did not ask for answers about this, but rather the following), I wanted to create a user with limited access.

The real problem here is that now I have no control over my remote installation of Kimsufi Ubuntu.

My current knowledge of Linux / Ubuntu: Obviously poor.

Where I am right now:
To regain control to a certain extent, I had to boot the OVH rescue mode from Kimsufi (Netboot> rescue64-pro). This apparently installs a separate operating system and gives me some provisional credentials. This allows me to see the HDD partitions of the machine with fdisk -l, but I know little more than I can do from here.

Current exact problem: I just do not know how to move from here to recover my ssh connection. I guess I need to find the folder where I ruined: "/ etc / ssh / sshd_config", edit it by deleting the lines I added according to the tutorial and restart ssh (waiting for the service to work again). I just do not know how to move between the partitions, find the file and edit it.