first of all, unplug all the appliances from whole property sockets and try to reset the RCD if RCD reset back then you don't need to go any farther and please leave us your feedback on this website link but if RCD does not reset than you need to investigate more if you are an electrician and you are reading this text then you can understand next paragraph if you are not qualified electrician then you should call someone who can come and sort out this electrical problem on 02034881842
RCD stands for residual current device always this have 2 poles one is for live wire and another ball is or neutral wire a single-phase connection RCD is comparing current of live and neutral wires all the time if any of the wire's current is not equal to each other's it means live and neutral parts of RCD will sense it and that will cause the RCD to trip so single-phase and three-phase RCD work in the same manner in single-phase one wire is comparing to another but in three-phase 3 live wires are comparing to one neutral wire so it means what all current which current is going into the system it should return back but not the voltages actual energy is stored in voltages but the quantity of the current stays same so that's why the returning current should be equal to the entering current so RCD helps to detect any leakage current into the system so