Configuring 'Back up Files and Directories' Policy
On the audited server, open the Local Security Policy snap-in: navigate to Start→Windows Administrative Tools (Windows Server 2016) or Administrative Tools (Windows 2012 R2 and below) →Local Security Policy.
Navigate to Security Settings → Local Policies→User Right Assignment.
Locate the Back up files and directories policy and double-click it.
In the Back up files and directories Properties dialog, click Add User or Group, specify the user that you want to define this policy for.