you don't need a jig ....
What I have found in working surfaces from automotive clay models to wood straight edges, is you need a "trained eye" for sighting down the edge. How can you train you eye is then the issue. Go out in your shop and start sight down edges until you think you have found a straight one. Now test it with a known straight edge from a factory scrap of hardboard or particle board or metal angle. Eventually you will be able to see where there are humps or valleys in the edge. Then you can decide to plane away in from each of the ends to reduce the valley depth, OR plane away the hump to get the edge straight.
A hand plane jig would be more trouble than it's worth. A good long straight edge would be a worthwhile investment, but it need not be .001" accurate. Some common sources for straight edged devices may be the 10 ft long barn door U channel for sliding doors at the home or hardware store. A 6 ft long aluminum level will work for many woodworking projects. The aluminum door casings off a storm door discarded at curbside are fairly straight. I have a 10 ft 2" square aluminum extrusion that I use for checking for "straight".
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)