I think it's important to discuss openly with your manager, especially if you want to grow within the company. The sooner the better

Make sure you give them plenty of notice, it can be hard to take on news like that but you definitely have to move on if your heart is not in it.

Downgrading sucks in most cases but it’s also needed sometimes. Think of it like the universe is showing you a new path and see if you can find some magic along the way. After all, if you accept something and you realise you don’t like it, you can always change it again