I accidentaly set incorrect configs, now I can't connect (details below)

I tried to set up Onlyoffice document server by following this guide on their website up to the line with
sudo echo "deb https://download.onlyoffice.com/repo/debian squeeze main" | sudo tee /etc/apt/sources.list.d/onlyoffice.list
but now my NextcloudPI (I installed it on and RPI 3, and I seriously forgot about the Pi not being able to run x86 programms) doesn’t work anymore, as trying to connect to it from my webbrowser now returns a “Website not reachable” error. Could someone please help me?