No dear bro
u cant
The best time to do tahajjud is before fajr, e.g 5am or 4am. Its the best as Allah will grant ur prayers as he will be at the Lowest heaven at this time. So its better to pray at this time. U cant do it at fajr time. However there is 2 rakaah sunnah b4 fajr, and Prophet mohammed said that this prayer is better than this world

But bro, i only do 2 rakaah, as truthfully i dunno how to do 4 rakaah nawafil? or 8 rakaah? How do i do this
Do i do 2 rakaah by 2 rakaah, and at the end of every two rakaah i say the salaam, and get up to pray the next set of 2 rakaah, and wat intention do i make in the start? Do i say"im making e.f 4 rakaah" and after each 2 rakaah, i get up and do the next 2 rakaah without doing another intention?