GB:
I haven't seen the model you are getting up close, so what I have to say may be way off-base.
Many of the newer compound crossbows don't have a separate string as such. The cable is continuous, with a serving where the bow cocks. It's very unlikely these will ever break, however, they can become worn, and need replacement. I believe that this work is done best by your dealer.
My Horton is the earlier version of the Explorer (with a wheel bracket instead of split limbs). This has an actual string that was 17" long. Each limb is attached with two limb bolts. The instructions that came with mine were to completely remove the "secondary" limb bolts (smaller in diameter), and then gradually loosen the primary limb bolts until everything was free enough to allow the string to be replaced. I was always careful to count the number of rotations on the bolts (using Allen Keys) when loosening them off, so that I could tighten them up to the same tension after changing the string.
Rick