If working from the top of the deck you may need to remove floor boards at either the rim, the ledger, or both, if separation is taking place in those areas. Next, with pole jacks you will need to jack the joists to the correct elevation and keep support under them while performing the draw to. With the deck supported where the separation is occurring. remove one joist hanger and install a heave metal angle on each side of the joist securing it tightly to the joist but allowing one-eight inch more than the separation from the ledger or the beam. Next, with strong hex heat screws tighten the angles part of the way to the ledger, the joist should move toward the ledger. Repeat this process with each joist. Once all of the joists are fixed with metal angles, go back and forth tightening the bolts until it draws all your joists flush to the ledger. Wallah! Your deck is repaired.
This method has never failed for me, even at times when I thought it might fail. I have saved my customers several thousands of dollars while making enough dollars for a good number of Starbucks coffees.