Do what Wilson Pickett did when recording "Land of 1000 Dances"
He forgot the words and sang "La-la-la-la-la la-la-la-la la-la-la-la-la-la....." The rest is history.

The secret of not forgetting your words is to learn the song in your teens. I can remember the words of all the songs from that era but now, in my late 60's, I can't remember what I did yesterday.