There are a few different ways that you can seal fabric paint on jeans. One way is to simply let the paint dry completely before wearing the jeans. This can take several hours or even days, depending on how thick the layer of paint is. Another way is to heat-set the paint using an iron. This will help to set the paint more quickly and prevent it from washing out over time. Finally, you can also use a clear sealant such as varnish or lacquer to protect the painted design.