@Sabur Mirza Thanks for posting in our Q&A.
A device joined to on-prem domain, and both joined to AAD means that it is a hybrid azure AD joined device. Currently, your devices are purely AAD joined. AAD joined cannot be changed to hybrid-AAD unless you use autopilot with hybrid AAD join profile or manually join the devices to on-prem domain.
To summarize: we can't directly convert.
Based on my understanding, it is suggested to remove the device from the existing Azure AD and then domain join them and let hybrid take over, or I would just recommend wiping them and do the hybrid join through autopilot.
https://learn.microsoft.com/en-us/autopilot/windows-autopilot-hybrid
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