There are some considerable users using their workgroup laptops as a Azure registered devices since there are accessing company resources. I was wondering whether I have a option to ask from them to rejoined a device as a Azure AD joined device. - Yes you do. Just take care of the licensing, MDM scope, enrollment restrictions.
When end user joining a new device to Azure I want to block join the device as a Azure register device and force them to join the device as a Azure AD Joined Device. - You can educate the users on the process, but honestly it will be easier if you just setup Autopilot.