There is no back migration from RAID-5 to 0
RAID configurations have different purposes, each configuration has a different function, and they work in a different way.
This would be the reason why going from one RAID configuration to another is limited.
In this case, the way to go would be to create the RAID configuration again with the needed drives for the desired RAID.
RAID 5: at least 3 drives.
RAID 0: at least 2 drives.