You must stand up and complete the missing fourth Rakah and then offer two prostrations after Salam.
If you didn’t do that, your prayer is invalid as you have dropped a pillar of prayer and you must repeat it.
You must stand up and complete the missing fourth Rakah and then offer two prostrations after Salam.
If you didn’t do that, your prayer is invalid as you have dropped a pillar of prayer and you must repeat it.