H4 to H1 COS with extension approved I140

Hi there ,
I was on H1 before and did H1 to H4 COS in April 2019. I have used my 6 years of H1 and my I140 got approved when i was on H4.
I am currently on H4 and it expires in May 2020 and I have approved I140 in 2019 from employer A .
I am looking for following options .Is both the options are available to me?

  1. to apply for H1 with employer A
  2. to apply for H1 with employer B, change of employer.

Am i eligible for H1 extension on the basis of approved I140 while i am on H4 ?
What do i need to do to continue working after May 2020 on H1?