Samvatsari is the last day of Paryushana. In practical sequence, it comes after the Chaumasi Pratikraman ( Chaumasi period/Chaumasi Pakhi is completed), i.e., at the end of the four-month Chaumasi cycle and then the annual Paryushana culminates with Samvatsari. In Śvetāmbara tradition, Samvatsari is observed as the final day of Paryushana (often falling in late August or September, on the Bhadrapada month in the Jain calendar). In Digambar tradition, their annual day of forgiveness is observed on Kshamavani, on a date that may differ from Śvetāmbara Samvatsari. The core idea remains: Samvatsari/Kshamavani marks the annual act of seeking and granting forgiveness at the end of the period of self-purification.

You can read more here