You can rename devices (aka “rooms”) in the app (unless Homekit renames them back).

You can edit the Group list in the app (delete named groups, create new ones).

You can edit unnamed groups at any time using the weird square-ish icon in the app.

Nothing here requires a reset of anything, but the details of your problems are vague so its hard to be sure.

Thanks for the response. I appreciate that details are a bit sketchy! As I understand it, I can name a room and define speakers within it. I can then balance these as appropriate. What I seem to have at the moment is an excess of defined rooms and no coordination of the speakers. I would like to delete all of these without losing connection to the speakers themselves and set up the rooms again. My understanding is that groups comprise more than one room. is this not correct?

I suspect you have it the wrong way round. In Sonos-speak a speaker -- or a stereo pair, or a home theatre setup -- is a ‘room’. Subwoofers are part of the ‘room’ that owns them.

You optionally ‘group’ ‘rooms’ ad hoc. https://support.sonos.com/en-gb/article/group-and-ungroup-rooms 

You can name a ‘room’ anything you choose, but it helps to use something meaningful.

The only way to ‘set up the rooms again’ from scratch is to factory reset them, which obviously disconnects them. You don’t want or need to do this.

So, if I have a home theatre setup with a playbase, subwoofer and stereo pair, this will not all be defined as one room?

A home theatre setup is a single ‘room’. The ‘stereo pair’, as you put it, would need to be bonded to the Playbase as surround speakers to be part of the setup.

If the ‘stereo pair’ is entirely separate from the Playbase setup they’d constitute a ‘room’ of their own.

Yes, that would be a single home theater ‘room’. If they aren’t all in a single room right now in your controller, you just would need to make them so, by following the instructions here:

https://support.sonos.com/en-us/article/add-surround-speakers-to-a-sonos-home-theater

and possibly here:

https://support.sonos.com/en-us/article/home-theater-or-stereo-pair-appears-as-not-configured

and finally here:

https://support.sonos.com/en-us/article/set-up-your-sonos-sub

So, I seem to have sound coming out of all speakers now, which is the main thing. Somehow though, I have an excess of rooms defined. Any idea how to delete these?

This makes no sense. An ‘excess’ of rooms? Those are your actual speakers. If you don’t want them then power them off.

What I mean is that that names such as “kitchen 2” have appeared, doubtless as a result of my own incorrect inputs. I simply want to delete these, but no great problem, as I can just ignore them

Those are your speakers. If you really want to ignore them, then reset them and sell them. Otherwise just rename them in Settings/System/<room>/Name.

Beware of Homekit renaming them back, of course: https://support.sonos.com/en-us/article/sonos-room-names-changing-on-their-own

Many thanks for the input