Change the inicial z home value

I am using a leapfrog creatr and i am using a POM filament, its really hard to have adhesion to the bed so know i am trying to put a thin layer of solid Pom in the bed soo that when the filament is printing the filament can stick in the Pom, for that i need to put the z value on the home position a little bit lower. How can i do that in the repetier 2.0.5?

Thanks.