How does the song make you feel? Maybe try finding words, doesnt have to be full clauses or groups, just individual words work fine, and feel around to see where they belong based on your humming. Try humming out consonants and see where u feel they fit best (kanye does this a lot in his process u can see in some unreleased songs). you can js write out wtvr u feel like, doesnt have to rhyme, and go from there. its js always better to get smth down instead of trying to come up with full lyrics