Ok so I've found the 1T hard drive I bought a few years ago and want to use it to back up the macbook

I've plugged it in and set it up, but it asks me if I want to erase it... I of course select no because it does have stuff on it I want to keep.... but it won't allow me to use it unless it is erased.

there are some folders of stuff on the drive that I don't need / want, but I can't delete them or remove them

does anyone know how I can still use it to back up the macbook without having to erase it? or how I can remove the folders on there that I don't need?

any help would be appreciated