Once you setup “Azure Attachment Storage” application in CRM; you can use the “Report and Admin” link to move the existing attachments from CRM to Azure Blob. But the drawback of that is after every few minutes it stops – due to the plugin limitations. And if you have lot of attachments it may take to couple of hours to couple of days to get all attachments moved.
I recently found a GitHub link to a solution created by Anil Kumar. Click here for the link to the solution. The readme file is pretty self-explanatory so I am not going to explain it here. The solution is a Logic App and it’s pretty sleek. You can install the solution on Azure just by clicking the button he has provided in the readme file.
Recommendation is to have RetrieveMultiple & Update plugin steps disabled on Note & ActivityMimeAttachment entities to avoid any performance issues