Find a bottle of nail polish remover; most women have a bottle somewhere in the bathroom. However, if you can't find one at home you can pick one up at any drug store, inexpensively.
Open the white out container and pour a few drops of nail polish remover into the white out. Be careful not to spill any on anything important; it is best to do this in a restroom over a sink since the opening to white out is so small and spills are almost inevitable.
Put the top back on the white out and shake it vigorously for a few seconds. Open it up and try it out. If the white out is still a little clumpy add a little more nail polish remover to dilute the white out even more. Shake the white out and try it again until you reach the desired consistency.