Put covers on songs

Hello guys, is there a way to put multiple covers on several songs? Or can it only be done manually one by one?
For example, I have 20 songs
5 are from the same album and therefore will have the same cover, but the other 15 are different from each other (different artist and album), that's what I mean, I saw that MusicBrainz and Discogs are there but it can't find the songs I have

Where would you find the covers?
In the file system or do you need a web source?

I copy the cover on Google, if I can't find it I search for it on SoundCloud or Spotify, I drag the URL of the cover or copy the specific image

You can drag&drop images directly from the browser onto the image field in the tag panel (and then save the modification).
This works for all selected files - they all get the same cover.
If you want to assign different covers to different files, you have to treat them individually.

I thought that was the only solution, thank you very much for the help, have a good day

There are other programs around like AlbumArtDownloader that can look for different covers for a set of files.
See e.g. here:

But for MP3tag the described way is the one.

Thank you very much for that recommendation, I will be checking it out.

How did I not know that?!? I've always used the right-click Add Image function.

Thanks!