What should I do if I forgot to say the Dhikr which is said between the two Sajdah in a Rak’ah and completed the rest of the prayer?

Before proceeding to knowing the answer to the question, one must first know the obligations of the prayer. One would then be acquainted with what needs to be done.

The obligations of the prayer:

The obligations of the prayer are eight.

1. All of the takbeeraath, excluding the opening takbeer

2. The dhikr said during Rukoo’ “سبحان ربي العظيم”

3. What the imam and the one who prays individually says upon getting up from Rukoo’ “سمع الله لمن حمده”

4. followed by “ربنا ولك الحمد” by everyone performing the prayer

5. the dhikr said during Sujoodh “سبحان ربي الأعلى”,

6. the dhikr said between the Sujoodh “رب اغفر لي”

7. sitting down for the first tashahud

8. the adhkaar said during the sitting of the first tashahud.

If any of the obligations are missed due to forgefulness, when the prostration of forgefulness is performed, the obligation will be achieved and the prayer will be complete.

Therefore, as mentioned in the question, the forgotten act was an obligation of the prayer. Hence before the Tasleem (giving Salaam at the end of prayer) one should perform the Sajdah of forgetfulness. That’s all that is required.