[Noob]

I have been soldering for many years and definitely use a good iron don't chance it with a cheap thing especially when soldering onto the esc, although they are designed to get hot holding a hot iron on them won't help so use solder flux even if the solder has a flux core dab a bit of flux on the contacts and flux then tin the wire ends also.
if the tip doesn't hold the solder and it bobbles off it it's probably time to change it as you will probably find it difficult to use.
I'm sure I have seen soldering jigs on hobby King or some where similar that might help also.