How to apply New H1b Extension/Amendment for 3 years while previous H1b amendment is pending

HI , I have a urgent situation and I need some advices asap Here is my case: I have H1b approved with Employer A working for Client A till May 6 2018. But in Jan 2017 I changed to client B and started working for Client B and so applied H1b amendment for Client B and that is still pending even now. Now few weeks back Client A called me back and I went back and started working to my Original Client A again as they gave me new project for 3 years. Now I want to apply H1b extension for 3 years but in premium only. Can I do that and what is the correct process to do that? I guess lots of people faced this situation after H1b amendment rule came can someone guide me?