Solution
1. Press [Additional Functions].
2. Press [Left cursor] or [Right cursor] to select [TX/RX SETTINGS], then press [OK].
3. Press [Left cursor] or [Right cursor] to select [TX/RX COMMON SET.], then press [OK].
4. Press [Left cursor] or [Right cursor] to select [RX SETTINGS], then press [OK].
5. Press [Left cursor] or [Right cursor] to select [TWO-SIDED PRINT], then press [OK].
6. Press [Left cursor] or [Right cursor] to select [ON], then press [OK].
7. Press [Stop/Reset] to return to the standby mode.