To be exact, your firmware need to be on 5.03 or lower. and hope that the HEN for 6.35 will be released next year.
Well, they will, it has been decided months ago by TN before 6.20 HEN was released yesterday. Though it might take a while.
They always say that. Then it doesn't come, then people will say "oh, they will release it with the NEXT firmware."
That likely to happen, since it was first decided on 6.31, but after 6.35 comes out, they want to release it for that firmware. and perhaps it might take a while considering some issues on 6.20 TN HEN.