The reset lever is found on switches with a low pressure lockout. They put these on low capacity wells so that if the water level drops below the pump inlet it locks out the pump instead of letting it run and possibly overheating. If your well doesn't have this problem then it probably isn't necessary. The low pressure lockout can be a nuisance, locking out the pump during high water usage or after power outages. If your switch doesn't have a reset lever, it could just be a bad switch (doubtful if it's new) or the problem is elsewhere.