Help compression fitting valve drip...Tips, Tricks, Fix

A handyman (yes I know) replaced four 1/2" under sink valves but did not have the tool to remove the nut and ferrule. He also used Teflon tape on the valve threads on both the compression fitting side and the feed line side. All 4 valves have a slow drip. What is the easiest quick fix. No I cannot have them professionally replaced. I had 2 downstairs replaced and it was very expensive and I can't afford these done by a pro. Should I remove all the thread tape, and run thread tape round the ferrule 3 times and reassemble? Please give me you hacks to remedy this until I can have this taken care of properly. TIA