Is that a Chinese clone?
First tip, shorten your 'location' it's taking me off the page and round the back of my PC.
Secondly, be very wary of any ad that claims:
That is essentially half a kilometre... Not bad at under 600fps.velocity 595 fps, trigger block safety, scope grooves cut in to breech, range approx 460 metres
Don't even consider changing the spring until you've got access to a chrono.
You may well end up putting a far worse one in.
Only way to zero it is to take it out to the field of your choice with a decent backstop, select your desired range (I'd start at 20m) and 'test & adjust'.