H1b visa to H4 conversion


I was on H1b from 2014 to 2016 and then moved to H4 EAD. Last year again I converted to H1b and the Max-out date is 05/2021. My employer is not filing for GC this year. So, I am planning to convert to H4 EAD so that I can retain my H1b time for few months. What is the quick and easy process to convert to H4 ead? After my conversion to H4, can I use my old EAD card which is valid through 12/2021. Please provide the inputs.