The best fix for a mosquito bite is to not get bitten! But once you've been bitten, the second best fix is heat.
If you can heat the lower layer of the skin to 42 degrees celsius for 5 seconds, that's usually enough to break down the chemicals it injects that make the bite so itchy!
A very quick soak in a natural hot spring, is wonderful for this. But I also a very hot shower to do the same.