I'm not very familiar with remote controls being mostly a tiller guy, but generally there are two setups I see for advancing the throttle in neutral. The one I see the most is where there is a lever on the top rear of the controls that you lift up. Pull it up all the way and leave the main throttle/shifter in the center position and it will advance the throttle while remaining in neutral. You can start the motor and then slowly lower the fast idle lever as it warms up, going all the way to the down position. This pic I googled of OMC controls is what I am referring to.
The other type of controls have a center button at the pivit point of the main control lever (would be where the circle of OMC lettering is in the pic). You depress that while pushing the lever forward and it advances the throttle cable while disconnecting the shift cable. It will automatically lock them back together to function normally once you return the lever to the centered position.