We apologize for the delay in response. From the looks of it you are looking for ways to transfer Data in from one managed instance to another.
Native Back up Restore definitely works for Managed Instance and is an option. Copy Only Back up and restoring them will be another option.
Additionally exporting and importing using BACPAC and also you can use replication with MI pub and sub architecture. There would be some testing required here to check what is best suited for your case. Please go through the documents. If you have any question regarding any of the cases, please revert.
Also if you think we are not able to answer to what you need, please elaborate your question further and we will be happy to help you.
Thanks
Navtej S