Open the folder and you'll find lots of pre-set tones to choose from.
Depending upon the pre-set list you open, some have a descriptive name, others only a number.

Click on one (say '159dk orange bl1'- below, if you have it on your list), then click the 'Load button. The effect is immediately apparent in your image - that is providing you have the Preview box ticked!

If you wish to choose another option then click 'Load' again and make another selection.

Should you wish to return to the starting point, then in the Duotone Options dialogue box (not the Load dialogue box) hold down the Alt key and notice that the 'Cancel' button changes to 'Reset' - click on this and you have the opening image. Alternatively one can click 'cancel' - but this takes the process back a stage or two and you'll have to re-load via Image > Mode etc.