It takes a bit longer for yeast to ferment from 1.090 than from lets say ~1.050 - 1.060.
What I would do is wait until it has finished fermenting (the gravity has not changed in at least 3 days), then look at if I have a problem or not.
If there is no problem (the FG is approximately where it should be), then just leave it for conditioning (transfer it to a conditioning keg/carboy) og bottle it and leave it to condition in the bottle.
If the yeast do not attenuate to the approximated FG, then I would try to find out why and take the appropriate actions.
I think that the yeast will finish attenuating properly and you will end up with the FG that you desire. Give it at least a week to finish.