Clean the Sabudana for any impurities.
Rinse the sabudana in water and drain all the excess water.
Now add just enough water. I.e. add water around ⅛ inch above the sabudana. I.e. there should just be a single ⅛ inch layer of water. (After 1 hour if you check, all the water must have been absorbed. If not, and if you have added excess water, just discard the water from the top)
Soak the sabudana well for 7-8 hours or overnight.
Next morning Boil the potatoes in a pressure cooker / Instant Pot or open pot as you prefer. (Can be done earlier day too)
Let them cool completely.
Once cooled, peel the potatoes and grate them using a fine or a box grater.
Add the soaked sabudana, red chilly powder, cumin seeds, and salt.
Give everything a nice mix.