Just to add, restore is fairly simple.
You need to create public blob storage credential protected with SAS on master database just like above.
Run RESTORE FILELISTONLY
statement and check if Managed Instance returns a list of the files in the backup.
And then you can finally restore the database using sample command like below:
RESTORE DATABASE tpcc2502
FROM URL = 'https://myacc.blob.core.windows.net/testcontainer/tpcc2501-4-1.bak',
URL = 'https://myacc.blob.core.windows.net/testcontainer/tpcc2501-4-2.bak',
URL = 'https://myacc.blob.core.windows.net/testcontainer/tpcc2501-4-3.bak',
URL = 'https://myacc.blob.core.windows.net/testcontainer/tpcc2501-4-4.bak'
Also regarding restoring on-premises, here is the blog - Lesson Learned #146: Restoring a backup from Azure SQL Managed Instance to OnPremises - Microsoft Tech Community