You need to create a SQL Server credential first to restore a database back up from Azure blob storage. A lot of writings can be found around the web on this. Most of them have used Azure Storage Account to create the credential in the first place. In this short post, I will be using SAS (Shared Access Signature) to create the credential first. So, here you go..
Following is a snapshot of a credential created using SAS. Identity will be SHARED ACCESS SIGNATURE and Password will be your <SAS token>.
Once, it is created you can now go to Restore database or Restore File or File-groups option
And finally use the credential created at the beginning to locate your back up file in Azure storage
Use your back up file’s URI in Shared Access Signature area.
If you like to use scripts to perform all these actions, you can follow this tutorial from Microsoft
Zahid's blog on Data Engineering and BI 