Can't Delete 'Free Space' after Removing Bootcamp

Hi everyone,

I've deleted my Bootcamp but a 'free space' has been left and essentially my 500GB is down to 400GB. (100GB has been used for Windows).

I've seen several threads about this but I'm scared to do something if the solutions marked aren't personalized on my case.

Let me know what you need from me so I get personalized solution as I don't want to mess up my MacBook even more lol.