Teebot Z Axis Offset Issue. Newbie Question

I own a teebot. I'm trying to use Pronterface and it has Slicer built in.

I know I have an offset issue. When I use G28 the Z states 3.5, if I do the G92 Z10 code and go down 1.4 the nozzle sits flush on the paper.

Now I've looked a number of help areas and I can't for the life of me save this new offset. Each time I print it still starts at 3.5 above. I know it's got to be something simple but I can't work it out.

Any help with this would be greatly appreciated.

Regards,

Peter