It won't have done any harm, but it won't have helped much either. What you really need to do is cut a small ammount of sponge off the cold water tank's filter, and stick that into the substrate in the Biorb's substrate. Leave it there untill the Biorb is cycled (has have zero readings for Ammonia and NitrIte for at least a week without water changes) and then return it to the cold water tank
There has been a combination of bad advise from the Biorb instructions and the LFS that's got you into this mess. If the shop won't co-operate on taking the fish back, just tell them that they gave you poor advise on what fish to start cycling a tank with, as numerous other fish keepers have told you that both Guppies and Neons are in need of a mature tank (at least 6 weeks old, preferable 6 months old) to do well, so sticking them into a new tank on their advise has lead to their death. If they aren't going to take them back and offer some form of help replacing the lost Guppy, you will not be calling back and will be advising your fish keeping friends to keep away also
If they remain un-co-operative, on the way out, ask why they didn't mention fish-less cycling also... Avoid an "all guns blazing" approach, but do put forward fairly loudly (no shouting mind) a strong argument as to why they were in the wrong. They should see sense soon enough
All the best
Rabbut