Ok... how to flush.... it doesn't matter WHAT overload you have! You want to run PH'd water equaling 3x the size of your pot ... so if you're growing in a 3 gallon container, you want to run 9 gallons of water through the pot (if it's a 5 gallon pot, then 15 gallons of water)... the LAST gallon of water to go through should contain about 1/2 your normal dose of nutes. You then let her dry out and get back to your water/feed/water/feed routine. Make sure that all water and all nutes are PH'd to between 6.0 and 6.5... if you don't have a PH pen, invest in one NOW... it's the single best investment you can make for your grows. I recommend Apera but lots of folks like Blue Lab.... It's also a good idea, when giving her water only, to water enough so that you get about 10-20% runoff... this will help clear out excess salts and nutes...
Good luck!