D-Link DSL-2790U User Manual page 111

Section 5 - Connect and Share a USB Device
Step 2 - Connect to the Web Configuration Utility. Navigate to Advanced >
Storage Service > Storage User Account.
Step 3 - Once you have arrived at Storage User Account Configuration click
Add to add a Storage User Account. Only one storage user account
may be configured.
Step 4 - The Add Storage User Account dialog will appear. Create a username
and password for your Storage User Account and click Apply.
Now that a Storage User Account has been created, you may connect to from
devices on your network.
D-Link DSL-2790U Wireless N300 ADSL2+ Modem Router User Manual 106