First download the Free Santoor n Dulcimer Player https://rdgaudio.com/santoor-n-dulcimer/
then put it into your DAW plugins directory. Extract the expansion and put them (.mse)
....\Santoor n Dulcimer.instruments or.
...\Santoor n Dulcimer\Contents\Resources for Mac.
Where to put Expansion Instruments files?
Ans: Put them.
....\Santoor n Dulcimer.instruments.
...\Santoor n Dulcimer\Contents\Resources.