Epson B 510DN - Manual (Page 135)

3. Insert the bottom side of the duplex unit first, and then attach the duplex unit.
Uninstalling the duplex unit
Follow the steps below to uninstall the duplex unit.
1. Turn off the printer.
2. Remove the duplex unit by pulling it while holding down the buttons on both sides of the duplex
unit.
B-310N/B-510DN User’s Guide
Installing Option 135