When you teleport to your corps friend on the battle field and your HQ is there, how do you get back..

To get back to your place is quite hard because you will need to have memorized where you teleported from to get to your friend. If you teleported from your corp base (where you corp command center is), you can use a "Corp teleport" to automatically teleport you back to the hive so long as your leader is there.

Next time I recommend you "bookmark" your position before you teleport out if you want to return back to that area!