Raising Voltage on Portable Generator - Does frequency need to be adjusted first?

I have a Robin Subaru 7500 portable generator that I use as an emergency backup. I use it to run two furnaces,, a fridge, a freezer and a well pump. It can handle them all, as well as the other miscellaneous electrical stuff in the house.

The surge power is 7300 and the full load is 6700 watts.

The AVR blew and I had it replaced. The power is running at 112 unloaded in both of the 120 volt outlets. I didn't check the 240 volt outlet, but I can with a multimeter. I checked the outlets with simple, plug in digital meters; these indicated that my utility power in the house was 120 volts, so they seem accurate.

I just tested it by plugging a 1700 watt hair dryer and a 1500 watt space heater into one outlet and a 1500 watt space heater into the other outlet.

On the outlet with both appliances connected, the voltage dropped to 110, perhaps to 109 volts for a moment. Correct me if I'm wrong, but I think I'm safe in that voltage range, but if I can easily raise it, I'd like to (more time on my hands with the Coronavirus freeze for projects like thhis ...).

On the outlet with only a 1500 watt space heater connected to it, the voltage was unchanged, or even went up a volt.

I found a Youtube video and some instructions on Champion's web site that showed how to adjust a screw on the AVR to increase the voltage, and it looks like a simple process.

However, I read on another site that I should first ensure that the frequency should be checked and adjusted first before modifying the voltage. I have no way of adjusting frequency - my multimeter doesn't do that.

Should I simply reset the frequency to 122 volts, or should I wait until the repair shop re-opens and have him check the frequency first?