Planer.
A jointer is only good for 1 face and one edge.

 

What Ger said. I would run it through the planer to bring that wedge down.

 

That's a job for a planer. With a planer sled, you can flatten stuff as wide as the planer. You use a flat board as a base, with a small stop block on one end. If the board is warped, you place small wedges between base and board until the board is stable. Don't take off too much. Better to run it through a couple of times until the side is flat, then you can run the otherside without the sled.

There are also very simple jigs you can make to hold an uneven edge in place to make a straight edge. Just make sure the blade is exactly 90to the table. You can also joint an edge with a router table with a split fence. Just add a spacer behind the outfeed side and and run the board through. But I like the table saw jig better. Plenty of videos on these jigs.

 

Find or make a strip of wood that is about the thickness of the difference between the two sides. It does not have to be very wide. Double side tape it to the thinner side of the board. Scotch brand thin tape will work. Run the wood through the jointer with the taped piece on the bottom.

 

Correct!

 

So the wider side would face the guide? Wouldn't the taped piece be cut off?

 

I do not think it makes a difference which edge is against the fence. Yes, the taped piece will get cut down as the thick edge is cut down. In theory, when the taped pieces is finally cut down to zero the other side of the board will have been reduced the amount of the thickness of the board. Be very careful. If you try to take off too much at once the cutters may grab the thin slice and jerk it off the board which will present a danger of removing parts of your fingers as well. Remember that you will want to apply a little more pressure to the side of the board that you are trying to make thinner because as the board gets thinner a wider and wider section of it will be removed. Scotch brand double sided tapes comes in two varieties. One states it is permanent but it is not. That is the one I would use. If you use the thicker tape (like mirror tape) you will have an issue when you get to the tape. Also, and this is the most important part, if you do not feel absolutely comfortable and safe doing this then do not do it. You may be able to find someone with a bandsaw or surface planer with a jig to perform the work. You have only been issued 10 fingers and 2 eyes. Wear safety goggles.