How to I change my z offset permanently?

I am using a Robo3d r1+. Do to a cracked print bed. I am having to use another sheet of glass with blue tape on top of the bed. Because of this I have to change my Z offset. How do I change that permanently in Astroprint so it knows to adjust due to the higher print bed?

You will probably get better support on their forums or webpage. A quick google search turned up this…