ehh, looks like you should be able to just pop the cover off, remove the screws and have a look-see inside; seems to be just a male coax connection...
is the cable not working? why does your client want to replace it?
if he/she's already got cable, the cable guy should have replaced it for them...
if it's in a building wired for cable, check with the maintenance guy, he
should also be able to swap in a new connector.
OTOH, it might just be a fiber-optic connector, not a cable connection; the wire looks awfully small for coax, coming out of the righthand side of the box, there...hmmm. is your client a new tenant or is this in a house? you dint say.
need more info!
thing about a switch-plate is...ya gotta have an in-the-wall or through-the-wall coax; switchplates are used to cover electrical outlets and cable/audio feeds, this on looks rather like an internet, not cable, connection installed by ATT (I have one that's similar, I think). I'd check on that first.
That looks more like a phone jack than an antenna jack.
The connections would be made on the side where there are markings on the top. Those markings look like one jack is for phone line 1 and the other for lines 1&2. That would allow a single or double line phone to connect.
If the jacks on the side don't look like phone jacks remove the cover. If you find a coax cable you should be able to just change the box. If the wire is flat 300 ohm antenna cable you will need a balun to convert that to coax. You might find a box with that built in.