As some other users said, is not a good option to mess with that voltage if you don't know what you're doing. Although, if you want to take a look, this is a common schematic of a relay controlled unit:
Relays have three pins: COM, NO, NC standing for Common, Normally Open and Normally Closed. It will depend on how you want to interface with the relay or relay module, you'll need to change your wiring.
Usually, you will cut one wire coming from the power and pass it to COM of relay, after that, grab the other side of the wire and put it on NO or NC. Applying or removing V on the correct pad (usually labeled as INx on modules) it will change the state of the relay, thus, changing the "state" of the thing connected through it.