The spice comes from pepper and no need to add rasam powder to it. Adjust the quantity of powder as per sourness of tamarind and how spicy you want. The remaining spice mix can be kept in an airtight container and can be used it for the regular rasam as well.
Jeera Milagu Rasam | Cumin Pepper Rasam https://themagicsaucepan.com/main-course/rasam/zeera-jeera-milagu-rasam