On the song page, you'll find a download link. Click on it to proceed to the download page.
If you prefer using a mobile app, you can download the Masstamilan app from the Google Play Store or Apple App Store. Follow these steps: Graamatthu Ponnu Song Download Masstamilan
Graamatthu Ponnu - Song by Viveck Ji & Shantra - Apple Music On the song page, you'll find a download link