Hi partner,
According to your description, if you are using D365 V9.X online, I recommend you to use "execel Online" feature.
For example I want to assign a customentity record to another user, I just need to click on "Open in excel online" and change the data and save.


And wait a minute, the owner will be changed to the user we selected before in excel online.

https://docs.microsoft.com/en-us/powerapps/user/export-to-excel-online
Add a custom ribbon on the form to open an excel file and get the update from excel to D365, this requirement needs a huge and complicated development project.
For the sake of system performance and data security, this is not recommended, If you really want to do this, you can check with the Microsoft partners.
Best Regards,
Leo