if you are not sure dont touch
all works within a bathroom are notifiable under part p, and should be carried out by a qualified electrician
there are many aspects to the fan and the connection of it
is it an extra low voltage fan (12v) or mains voltage 230v
what zone is it positioned in
is there rcd protection to the circuit it may be connected to
is there supplementry bonding to the bathroom
how is the fan to be controlled, timed, manual operation, humidistat control, pir controlled
if its a timer type it will have three wires and maybe an earth conductor
any of the others it will have just two wires and maybe an earth conductor
and you thought electrics was simple !!!