(It’s rather by accident that I’ve seen your post, because I migrated to a new account. You can find me at @simplymike)
I’ve written a tutorial on how to claim back your voting power from MinnowSupport Project.
It works the same for Minnowbooster: you simply send them a new delegation of 0SP.
I think most services work like that...
If you’re following a curation trail somewhere, make sure you unfollow it.
To see to which services you have delegated, you can use steemworld.com