An RCD is also known as a trip swtich. They are electrical safety devices in your consumer unit which help prevent electric shocks which could kill you. They should be tested every six months but people usually don’t because any clocks connected to the mains will need to be reset. However, all clocks will need resetting in March and October when we change from GMT to anyway so this is a good time to do it.
So during the morning after the time change, before you reset the clocks, I suggest you press the test button on your RCDs..
They should trip off, then you can push the switch back up to turn them on. (Some MK branded ones will need pushing down before pushing back up again).
You should have one or more RCDs in your consumer unit. They may be labelled RCCB instead. Or you may have many RCBOs. They will all have a test switch on them and they should all trip off when the test button is pressed.
Some installations may have an RCD which is separate from the consumer unit, and these should be tested too.
If they don’t trip off, it’s worth getting an electrician in to check it out.