If someone said the Tasleem after two Rak'ahs in the Dhuhr prayer and then remembered, do they resume the prayer or build upon what has passed?

If someone says the taslim forgetfully before completing their prayer, then if they remember after a short time, they should complete their prayer and perform the prostration of forgetfulness (sujud al-sahw). However, if a long time has passed, they must restart the prayer anew.