As I am sure you are already aware, you can now submit requests directly to the Dynamics Service Engineering (DSE) team by using Lifecycle Services (LCS).
Submit a request to the Dynamics Service Engineering team
https://docs.microsoft.com/en-us/dynamics365/unified-operations/dev-itpro/lifecycle-services/submit-request-dynamics-service-engineering-team
One of the request types that you can select is the Database refresh, which includes the ability to refresh a database from Production to Sandbox.
When you log this type of request on LCS, you will see a list of Terms and Conditions which you should be familiar with so you know what will happen and what you need to do when DSE have completed their actions and the Database refresh is listed as Succeeded.
I am not going to include a screenshot of the current Terms and Conditions here as they may change over time and you should refer to the most up to date information each time you request a Database refresh, but I would like to draw your attention to one particularly important point regarding user access:
// Currently point 2a in the Terms and conditions as of 29th August 2017
All users except the Admin user have been disabled. This process allows the Admin user to delete or obfuscate data before allowing other users back into the system.
In order to provide your users with access to a recently refreshed sandbox environment, you need to enable user access for them.