Yamaha DTX-PRO Reference Manual page 84

KIT Mode
4.
Strike the drum pad to which you wish to import an audio file.
Make sure that the name of the pad you struck is shown on the Inst selection screen.
5.
Press the button below "IMPORT" ([F3]).
The IMPORT screen appears.
6.
Use the [–][+] controllers to select a file to import.
You can change the pad selection by pressing the "TRG" button ([F2]), or by striking the pad.
or
Name of the audio file to be imported
Pad to be assigned
DTX-PRO Reference Manual 84