parse is used to transform a string into a number (like u32).
From the error, it sounds like you already have a number, so you don't need to call "parse." Rust variables have types that are known at compile time, so you don't need to call functions to check their types.
Without seeing your whole function, I can’t really tell you how to fix it. Please paste a more complete example or share a link from the playground if you have more questions.