A friend, actually a very good singer songwriter, asked me for suggestions on turning an idea into a song. I said:
Take a song you like, sing new words to the same tune, then change the tune, then change the chords. Keep the structure. There you go.
Or my technique, walk around town with it, singing quietly to yourself. People look strangely. Ignore them. Do this regularly for at least three or four years then write it down. In another year or two you’ll have your song.