What can I do about abutment lost off my implant while it's healing?

It’s most likely just a healing cap, not an abutment. Go see your dentist to see what was lost and go from there. It’s not your fault is a part cake dislodged. Your dentist installed it and it should’ve been secure.

There is nothing to worry about.  Although the gum tissue will cover the implant rapidly, you can see your surgeon to replace it at anytime.  

Please go back to your Implantologist and get another Healing abutment fixed ,do not worry if the gums have closed off , Implantologist will open up the gums and fix a new one. 

I'm sure you mean the healing cap. I place the abutment  only if you are getting provisional or definitive crowns. If you lost it, you have to get another one.