Take the front off,,, and inside where all the electronic circuit bord is,,, at the bottom, and at the top,, there are two round things coloured blue,,, both with white inside and a tiny slot,,, you will need a tiny screwdriver .
The little white slots move like turning a screw, I can't tell you how far to turn them,, it's a case of trial and error,,, you can usually adjust the calibration with just he bottom one,,, but sometimes you need to feck around with the top one as well.
Of course first thing is to put a batterie in the collar and put it on the floor, then stand on a chair or s