One song from my playlist on Google to add as a ringtone for my contacts
AFAIK you cannot. GP songs are encrypted and inaccessible for things like ringtones.
Maybe try looking for the song on Zedge?
They make apps for that, if I understand what you’re talking about. I think mines just called ringtone maker.
Well, my phone lets me take music straight from any I’ve put on there myself and set them as ringtones. Pretty sure it’s a standard feature with most phones these days. Granted, this doesn’t answer your question, but if you’re able to find an MP3 for the song in question and put it into your phone directly you should be good.
I second using the Zedge app. It’s a good place to find ringtones for everything.