Go to a vet. Find one that is reputable in exotic. If you can, have a culture sent out to rule out nidovirus. Morelia are slow to show visual signs of distress and disease so once you see signs of RI, it needs a vet's treatment. Do not do DIY fogger treatments or pointless attempts at home remedies like eucalyptus oil.

Make sure the enclosure is not using bark or coconut fiber substrate while treating. Paper towel or other disposable clean liner only. Raise temperatures slightly to increase immune responses and keep humidity down while treating. Make a vet appointment as soon as you can. If you just ordered the snake however see if you can return it for a full refund, you should not have to take on the responsibility of any illness if you just bought it. Also, that was not a reputable breeder if they sold you an ill snake. Any reputable breeder would constantly monitor for signs of illness and never sell something immunocompromised.

Here is this site's vet list to find one.

https://ball-pythons.net/forums/show...d-Exotics-Vets