Oki C9300dn User Manual page 112

Click on the [General] tab, [Printing Preferences] button and
6.
[Paper/Quality] tab then select the multi purpose tray in
[Paper Source].
Click on [OK] twice and close the printer dialogue box.
7.
PCL printer driver:
Click on the [General] tab, [Printing Preferences] button, then
1.
[Setup] tab.
OR
Click on the [Advanced] tab, [Printing Defaults] button, then
[Setup] tab.
Select User Defined in [Size].
2.
OPERATION > 112