Oki C5300n User Manual page 61

If you select a media type (e.g. Plain), the printer takes paper from a
tray that contains that type of media. To assign media types to
specific paper trays, you need to use the printer' s operator panel.
If you choose Auto Select, the printer automatically chooses a tray in
the printer that contains the correct size of paper.
If you choose a paper source manually, ensure that the paper tray in
the printer contains paper of the correct size.
MAC OS 9.X / CLASSIC > 61