@Swahela Mulla, Thanks for posting in Q&A. From your description, I know there are some Intune managed devices which you want change from other join type to Azure AD join.
Based on my researching, I don't find the method to do this. I think you need to unenroll these devices and re-enroll into Intune using Autopilot Azure AD join enrollment method or Azure Active Directory Join with automatic enrollment method (The devices will be Azure AD joined after the enrollment).
Thanks for your understanding.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.