Voluntary omission of the prayer of tawaf invalidates the Hajj. But in case it occurs due to ignorance of the rule or due to a lapse, one should return to the Masjid al-Haram and offer the prayer if one is not far away and can offer the prayer in its place without hardship. But if one has gone far away from Makkah, one should perform it wherever one is reminded.   _{Your Comment}