How to clear a register

[Harry P]

I'm probably blind but when looking through the register related
commands under C-h b.  I don't see something to delete or clear or
even edit a register once you've inserted something in it.

I had no better luck with M-x apropos <ret> register <ret>
Searching for delete, clear, dump, remove.

I see how (using a prefix arg) I can delete a region from the source
when its sent to a register but no way to mess with what is inside a
register.  Don't even see a way to overwrite a register.

Using the i (index) search in the emacs manual to get to the section
on registers... I still see nothing about editing, deleting.

So, I've pretty well exhausted my knowledge of how to find something in
emacs documentation.

Is there any way provided to delete or edit or at least overwrite, text
in a register?