Abu Hurairah (ra) reported the Messenger of Allah (saws) as saying:
If anyone obtains a rak’ah in the prayer (along with the imam), (it is as) he has obtained the whole prayer.
Sunan Abi Dawud 1121
In-book : Book 2, Hadith 732
This is mercy of Almighty Allah upon his slave that he gave us relaxation as well as comfort in our life
From the above mentioned hadees it is clear that if we late for any congregation period especially in case of Friday prayer and we are able to find only a part of prayer then we should complete what we had missed, and it will as we have found complete Prayer
In case if a person missed complete player with congregation in Friday that is Friday prayer then if he is able to reach any near by mosque he can go there and if it is difficult for him he should pray Johar prayer 4 reka’t Obligatory Prayer of johar