What is the ruling if a worshipper completes the prayer but then realizes they missed one prostration from either the first or the second unit, without knowing which one?

Primary text

If the worshipper realizes after completing the prayer that they missed one prostration from either unit, or doubts whether they missed it, the ruling is the same: they must treat the missing prostration as belonging to the first unit and then perform an entire replacement unit (rak'ah). There are two views regarding whether this renders the prayer valid as the Jumu'ah prayer, depending on the differing narrations concerning the initial realization.