If you don't have dried red chilli, you can use chilli powder. Use around 2 tsp (adjust to suit your taste). Also, you can increase or reduce the qty of tamarind to suit your taste. But first do a taste test of tamarind, some variety tends to be very strong. Also, it's better to add salt after tasting tamarind, because some tamarinds can be very salty. So, adjust the qty of salt accordingly. Try to grind the chammanthi without water, if it's possible.