the main thing u can do is replace the air filter .pull out the old one and match it with a new one and replace it

Depends on what kind of heating and cooling system you have. You say “my electric bill”, so does that mean you have electric heat? When you say it’s “one HVAC heating and cooling” unit…is that a heat pump? Or a furnace? Gas? Propane? Oil? Electric?
Nuclear?

Assuming it is gas heat, there is very little to adjust on such a heater once it is set up. The air/gas mix is initially set and unless the heater was hit by a meteor or something, it’s probably fine. The filter should be changed periodically, but even if it is not changed as often as it should be, it won’t significantly affect your bill. If it’s pretty dirty, the fan uses less energy, because it moves less air, the temperature of the air that is discharged is higher. The same dirty filter during the cooling season can cause more trouble, because the lack of airflow can frost up your coil and stop the A/C from working.