I would be glad to help. The most common reason for the wrong tray being selected for printing is due to the paper size chosen for that particular tray, and using that paper size when you are printing. Please make sure your printer has the correct paper type listed for each tray. You can do this by looking at at pages 166-167 of the Windows manual if you are using Windows:
or pages 164-165 of the Mac manual if you are using an Apple computer:
Then when you print, go into print settings and select the paper type you wish to print from, and it should choose the tray that is using that type of paper. Let me know if this does not resolve your issue, or if you are having trouble with the solution.