Covenant of Prophets? can someone explain this ayat

>- And (remember) when Allah took the Covenant of the Prophets, saying: "Take whatever I gave you from the Book and Hikmah (understanding of the Laws of Allah, etc.), and afterwards there will come to you a Messenger (Muhammad SAW) confirming what is with you; you must, then, believe in him and help him." Allah said: "Do you agree (to it) and will you take up My Covenant (which I conclude with you)?" They said: "We agree." He said: "Then bear witness; and I am with you among the witnesses (for this)." 3:81 - Translation by Muhsin Khan. how come Rasul (Muhammad(S)) went to each Prophet in past and did confirmation and how Prophets of past helped Muhammad(S) as mentioned in ayat? **My understanding so far**: If Allah says one Messenger went and did confirmation of The Book and Wisdom with all Prophets then we can't say 'any' one of the messenger went from 300+ messengers (there is no proof in Quran about 300+ messengers). Allah only talked about 19 Prophets and few messengers in Quran. Prophet are normally Humans in Quran. Messenger is either a human or Prophet or Angel. It may be possible that Muhammad(S) went as an Angel or Spirit (Allah knows best). Quran doesn't say Muhammad(S) was last, but Khatam-un-Nabiyeen (Seal/Confirm of Prophets).He is confirming what Prophets got. In Surah Isra/1 Allah took his servant in night from A to B we don't know how but Allah took him. We can assume i think. If we assume Muhammad(S) as last then we would be confused how the Last one went to each Prophet? Khatum means not last it means Seal/Stamp. 2:7 Allah has set a seal upon their hearts (Khatum word is used). If we say he was seal/stamp/confirmation, then we can say in 3/81 Muhammad(S) was the one that did confirmation with Prophets. Allah knows best. I would love to hear the answer from someone that is correct understanding of this ayat according to Quranic ayats.