Maybe you can do something like this . . .
First, find out when x increments by 1, what is increment in frequency (call this the step size)
Second, find out what is the frequency when x = 1 (call this the minimum frequency).
Then to find actual frequency from x you can do some math like below:
actual frequency = minimum frequency + (x * step size)
Now you can print the actual frequency on the lcd using LCDOUT (assuming you are using a HD44780 based LCD display).