It's a hassle. Here's what you do: Play the song on your computer alongside some additional music. It'll be cleaned up in post-production. I like techno for this purpose. Sing along to the lyrics, getting them wrong on purpose. Again, it'll be cleaned up in post-production. Record all three together on your phone. The recording quality doesn't matter; it'll be cleaned up in post. Now upload it and fix the lyrics and cover. Hopefully it'll be easier in the future. You can also write them down, but I've never heard of that working; it's just what the site tells you to do.
