Simply call Delta and give them your OnePass number or present your OnePass card upon check-in. The miles will credit to your OnePass account. Different fares earn different amounts of Elite qualfying miles. There are basically no OnePass Elite benefits on Delta other than priority boarding privileges and ability to check-in at the line designated for Medallion members. Presidents Club members can access the Crown Room when presenting their card and a Delta boarding pass.

These benefits do NOT apply to SONG-operated flights.

I suggest reading the OnePass website which spells out the details for you.