Back in Black
Back in Black is a great song to play on single strings and get used to alternate picking and moving from string to string.
Louie, Louie
Louie, Louie is great for slowly stepping in to playing frets, while still using mostly open strings.
Believer
Believer can be played all on one string. Try to use a different finger on the larger transitions.
Centuries
Centuries combines open strings, changing frets, and changing strings.
Old Town Road
Old Town Road uses only two strings, but some of the movement is a little faster and maybe challenging for beginners.
Twinkle, Twinkle Little Star
This is a version of Twinkle Twinkle Little Star that can be played using only one string.