I DIY my juices. When I try a new mix I always try it in an RDA first. If the juice isn't what I'm expecting then I rework my recipe.
If you're referring a garbage retail juice then I would dump it. You can try adding a small amount of a new juice and see if its flavor eventually overtakes the old juice on the wick and coil. Some strong juices will leave a residual flavor. In that case I would try a new wick first.
Before you change the coil do a few dry burns on it. In between dry burns run the coil under water. Better yet, use some unflavored between dry burns.
Worst case, if the garbage juice was a very strong flavor you'll have to, as
@Territoo said, take your tank apart and give it a thorough cleaning.