If you are not familiar with the standard Inscript keyboard layout:
If you have an old document typed in an older (non-Unicode) version of Rohini: Assamese Rohini Font Download
Google Fonts hosts an optimized version of Rohini as part of their Early Access or Noto collection. To get the pure Assamese Rohini, you can visit the Google Fonts repository and search for "Rohini." If you are not familiar with the standard