The bar with the dot on the top (the highest bar) means that the channel is saturated and Bolt will not be trying to use this frequency to connect. Each bar is 20MHz channel, so two adjacent bars need to not have the dot in order for the Bolt to try to use the frequency (most Bolts use 40MHz channels except for Bolt 3000 in 20MHz mode).
The “+” on the spectrum analyzer doesn’t mean that the Bolt is broadcasting on that frequency, it means that the frequency is enabled for usage by the Bolt. This is the same that you would see in the “Channel Selection” menu but integrated into the spectrum analyzer screen.
On the Bolt 500 you will not be able to adjust frequencies, but you could at least check why the Bolt 500 set is not connecting (if it is because all channels in the area are busy, or the signal it too weak, etc.).
Please note that you will want to turn off the TX when measuring the Spectrum, especially if the TX is close to the RX.