I am in a rented unit, the power went off the other day and now I can't get my aircon split system (no manuals provided) to work again
Normally in your situation I would call the owner and ask for instructions. You could request the owner to send a technician and get it up as a tenant you cannot be denied use of the aircon if that is part of your lease benefit.
We cannot help you much at fixya.com without knowing the make and model number of the aircon unit. Usually with split systems I could suggest you turn the mains power off at the circuit breaker, wait a few seconds and then turn back on. Then go to the internal unit and with remote control start the unit. See if everything comes back to normal.