Connex CX-4300HP CB Radio "bump knob" Questions

i have a connex 4300 hp, with a new antanna i left the cb shop and it worked great got out over 15 miles or so but on the weekends i clean out my truck and take my cb home so no one will steal it and ...

...Knob while holding his MIC Button. What does that do? Also, he said he was adjusting his RF Gain and Squelch to help his transmit audio. But those adjustment are for RECEIVE.. Please correct me if I ...