It depends on the client you're using.
In amethyst you click on their profile then the 3 dots in the upper left corner and you can block them.
As far as I know there's no way to make them unfollow you.
Discussion
Upper right corner, that is
I am using the iPhone version which is Damus I believe? Sorry new to all this.
I don't have an iPhone, but I'm pretty sure the procedure is similar
On my version the only options with the dots are report, mute or share. Must still be getting worked on.
