That "variable resistor" is called a potentiometer, or pot. you turn the screw to increase or decrease the resistance. It's proportional, so if you know how far off your tach is, Greg can probably tell you how many turns to make and which direction to make them. If it's easy to get at, and you know the pre-replacement RPM at idle, you can adjust until you get that number.

Hi Lynn,
So what did Greg have to say about the 7k written on the potentiometer? Seeing how you already replaced the board and drilled a hole in the housing, I'd go ahead and remove the extra resistor if it were me. The pot will make up for any variance from removing it I'm sure.
If you wanted to know what the resistor value is, I was taught this to remember the stripe values back in the day: Bad Boys Rape Our Young Girls But Violet Gives Willingly - Get Some Now. Black, Brown, Red, Orange, Yellow, Green, Blue, Violet Grey, White (Gold Silver None are the tolerances). I know, I know, real PC lol