Re-enabling Third Party Entries in sources.list through SSH (remotely)

Wondering how you can do this? Upgraded from version 16(.?) to 20.04.3 LTS, and I got this message, I use it for a fair bit of port-forwarding and streaming and etc, using it as a media server, and I'm just wondering how to do this?

I didn't initially set this up, but yeah I am curious as it does say

Some third-party entries in your sources.list were disabled. You can re-enable them after the upgrade with the 'software-properties' tool or your package manager.

A lot of people say to go to the Ubuntu Software Centre, but I think you can only do that on the machine itself, the other thing I tried was nano'ing into /etc/apt/sources.list but I can't see really any third party entries in there.

Anyone know how to re-enable them remotely?

You have to visit /etc/apt/sources.list.d directory, locate *.list files here and find lines ending with # disabled on upgrade to focal.

Be careful - some third-party repositories may not have packages for current Ubuntu versions.
For example uncommenting lines like "# deb http://ppa.launchpad.net/notepadqq-team/notepadqq/ubuntu focal main # disabled on upgrade to focal" will lead to 404 error (does not have a Release file.) on next sudo apt-get update as this PPA does not have packages for 20.04 LTS (focal fossa).
So safe method is to visit http://ppa.launchpad.net/notepadqq-team/notepadqq/ubuntu link by web-browser and check the existence of dists/focal folder here. If focal folder exists in dists folder then you can uncomment line safely and then run sudo apt-get update followed by sudo apt-get dist-upgrade to get upgrades with new dependencies.