What was your recipe and mash profile including temps and times. To properly respond I need to see if you have the fermentable sugars to get down to 1.020, that is 83 to 84% attenuation and you need to modify your normal procedures to achieve those levels.
Based on a "normal" mash (whatever that is) I would expect something in the 1.035 range, If your mash was warm and/or short I would expect something around 1.050 for a FG.
Fixes depend on your end goal and your mash profile. You may need an enzyme addition to produce more fermentable sugars, I do not recommend this except in extreme circumstances.
Finally the best way to unstick a stuck fermentation (not a completed fermentation, and I don't know which this is) is to add a growler FULL of thick slurry, the best is from your friendly neighborhood brew pub. Any clean ACTIVE yeast will do. The idea is to add a full working population of yeast (you don't want to GROW yeast at this stage) so adding a starter is IMHO not sufficient.