How to replace a micro USB port solder pad that tore off

A picture would be helpful.

Getting a new, dedicated pad isn't really worth the effort,

If any of the old pad is still attached or there is a visible bit of copper leading to the pad you could try making a new one,

Fold a very fine wire into a U shape, close the two prong ends, twist the two prong ends together a tiny bit (just enough to prevent them from separating) tin them, and then solder the two twisted together prongs to whatever exposed bit of copper is left from the pad. you should be able to carefully solder the port onto your makeshift pad, be sure not to overheat it or you will remelt the solder holding it to the board and you will have to do it all over again. (prevent remelting by holding a metal object to the wire in between where you've attached it to the board, and where you are currently soldering)

Make sure you use a Rosin based flux, doing this is near impossible without it

If there isn't any copper visible you could try taking the tip of your soldering iron and melting a bit of the plastic off the board, be very careful doing this though.

Hope this helped, Good luck!