Couple of suggestions:
1. Gently stir or shake / swirl it to get the lees (and yeast) back in suspension.
2. Move it to a slightly warmer location. Add 5 degrees F or so.
Give it time, a week or so and check SG. If still stuck...
3. Check pH. If low < 3.0 add Potasium Bicarbonate.
4. (Last...