how can i move the songs in a playlist back to the song library

running ITunes on WIN 10 Pro 64 Bit VERSION 10.0.15063

Somehow, i have managed to move songs by a single artist into a playlist, BUT

now those songs are no longer showing up in the "song" playlist (THEY DO SHOW WITHIN THE ARTIST PLAYIST)

They are not included in what is displayed in the song playlist, nor or they automatically played when i am playing music from the song playlist.

HOW CAN I COPY THOSSE 3 SONGS BACK INTO THE SONG PLAYLIST (OR GET THEM TO

SHOW UP AND PLAY ALONG WITH ALL OTHER SONGS?

And how might I have "lost" them from th Song List in the first place ?