What's this jell flux? How does that work with regard to part removal? Never heard of using flux for part removal but if it eases the process then it sounds like really good stuff to have. Removing some parts using the hot air tool can be tricky when you try not to thermally over stress the part.
I don't know about gel flux, but considering your location, I suspect you need to use and fix lead-free tin-solder joints. ChipQuik is an American brand for a spooled solder-like material that makes a low-melting alloy when added to solder. You add this solder, then remove the component with much less heat. Excess is wiped off the board with solder wick. I suspect is is basically a gallium/bismuth solder. Almost any very-low temperature alloy should work. Avoid alloys with indium, if you have anything with gold plating on it.
Flux prevents oxidation of the base metal, soldering or desoldering oxidation is bad. Oxides formed during (de)solder prevent heat flow, generally speaking oxides are insulators!
This video illustrates liquid flux use in standard and hot air work.
It shows soldering rather then desoldering. The liquid flux helps float the chip during soldering to center it. It helps distribute heat during both processes.