Inherited sonos speakers, can i use them?

Can anyone offer me advice here?

Factory Reset. You may need to temporarily wire these units to your network.

You’ll want to setup a new system as you get the first unit online. The remaining units will be added to an existing system (the first unit).

Transfer system will probably not work because you will need the original user name and password. Also, if the previous owner is using other units, you would not want to transfer these units to you.

Sorry, I'll need to make multiple posts, as I tried in a single one and got an error.

Your speaker has a mic, so it's a Sonos One, not the Sonos One SL:

This is the back of the Sonos One, showing the Join button (#1), which you'll need to press to reset the speaker:

Note the Join button is just above the Ethernet port (or below, as your speaker is mounted upside down)

The Join button should be behind this hole and you can try pressing it with a small stick:

If you can't press the Join button, then the other option is to remove the speaker from the mount. You'll need to slide the mount open, releasing the socket and/or screw below. You can do that with either a ratchet or a wrench:

If you can't press the Join button, then the other option is to remove the speaker from the mount. You'll need to slide the mount open, releasing the socket and/or screw below. You can do that with either a ratchet or a wrench:

 

I have tried everything to get this screw to turn, with no luck. The screw head that you circled is mine, i put it there, the trouble is, from this screw head to the wall/ceiling is about 6cm, there is no room for a proper screwdriver to get in. I have tons of wrench's, ratchets, etc, but nothing i have tried can get a grip on this and make it turn. The downstairs bathroom speaker will be even worse to get off the mount, its tucked in real tight to the top corner!

Absolute nightmare, this is driving me insane. 

i dont think the join button is behind the top hole