You will never get the coil to perform exactly like a new coil, but you might be able to extend the life of an old coil with this method.
Remove the coil from the base unit. Take the coil and rinse it under HOT water. Keep running hot water through the coil till the wicking material is as clean as you can get it.
Put the coil back into the base unit and screw it onto a battery.
Pulse the battery repeatability. You will get steam generated from heating the coil and the water that is in the wicking materal. Keep pulsing the battery, till no more steam is generated.
Continue pulsing the battery, till the wire inside starts to glow. This help burn off the caramelized juice on the wire.
Once there is no more somke being produced you can fill your tank with your juice and screw the base, coil assembly back on to the tank.
You can then start vaping your juice. WARNING: You will get a burnt taste for a while. Just mouth hit and exhale the vapor repeatedly till the burnt flavor diminishes. You might have to go through a few milliliters of juice to get rid of the burnt taste.
Once the flavor of your juice returns, you can vape normally.