You need a temperature tester to be able to tell the temperature differences.

Which soldering iron did you get?

Theres things like this https://www.amazon.com/YWBL-WH-Soldering-Temperature-Thermometer-Measuring/dp/B081GGBDP1/ made specifically to measure an iron, no idea how good the cheap ones are. Or you could try turning the temp up slowly and see if it gets easier to melt. Also look up the melting point of the solder your using, lead free takes a little more heat.