Help to adjust gplab ( genetic programming) to initialize the population

Hallo, i am doing signal analysis, i have some features ( F1,F2,F3... and so on,like rms etc) and i would like to extract an advanced feature (eg. F = 3× F29 + F30 + F42 × F35) using genetic programming, with monotonicity as fitness function ( for the advanced feature F monotonicity is 1). I am wondering how could I use gplab software to imprort my data (to initialize the population) and fitness function I have created, in order to adjust the inputs to the specific requirements. Any help could be usefull. Thank you in advance.