Make sure your swasplate is level. That is probably the cause. First start by unplugging the motors. Then plug the battery in and go to half throttle and flip the switch on the top right of the transmitter towards you. Then you will probably see that the swashplate isn't level. Most likely you will need to lengthen the pushrod on the LEFT side of the helicopter looking from the back. And it is the pushrod on the outside of the swashplate.

The top right switch is the idle up switch. That adjusts the pitch and throttle curves, so you get negative pitch below half stick and the throttle also starts to increase below half stick. That is when the switch is torwards you. Then when it is away the throttle curve is linear and there isn't that much negative pitch.

The rotary knob in front of the idle up switch is for the gain on an external gyro.

Don't worry about the servo reversing switchs as those should already be in the right spot.

The four sliding switches by the sticks are called the trim. I now realize those aren't stated in the manual. The bottom left one is for the rudder. Move it right and the rudder will want to go to the right more. The one to the right of the throttle stick is for the throttle trim. You need that at the very bottom when you plug the battery in or it won't arm. If you increase that you will get more throttle. The one to the left of the right stick is the elevator trim. If you push it forward the helicopter will want to tip forward more. Then the one right below the right stick is the aileron trim. Move that to the right and the helicopter will want to tilt more to the right. This is the one you could move more to the right to keep it from drifting. But you should keep most of those in the center and do mechanical adjustments instead.

I can't remember what the top left rotary switch does, but it should affect either pitch or throttle curve in idle up mode.

Hope that helps.

Nick