Flatten out all air bubbles so that the cover sits flat on the water
Using your pool as a template, take a pair of ordinary household scissors (the sharper the better!) and with someone holding cover in position, cut the edge of the cover so that it sits flat on the water with about 50 - 75mm rising up the side of the pool (but not necessary the top edge of the pool).
If required, you can:
Cut the cover back to waterline, however, wait 2-3 weeks after initial cut for it to settle down. The cover can shrink in the length in the first couple of weeks, so don’t make the initial cut too short.
Cut two vertical slits in the cover upturn, either side of your skimmer box, fold the flap you have created into the skimmer box, therefore allowing you to hose debris off the top of the cover into the skimmer box.