SnapshotManager.restoreSnapshot

Restores the state of all forms to the specified snapshot. This includes the current form and any other forms that may be in the form "stack" when call form has been used. The user can then continue working with the restored data.

Further documentation.

Javascript example:

 var snapshotId = fields.SNAPSHOT_ID.value;
 try
 {
      system.snapshotManager.restoreSnapshot(snapshotId);
 }
 catch(e)
 {
      log("Error restoring snapshot: " + e);
 }