Maybe it is good that the owner is not here, ah? Many of us tend to think that everyone understands everything. I started to hate these terms "pack order", "dominance", "submission", etc. One seems doesn't fit into the other.
Here, in this case, which is very typical, there are thousands of absolutely the same cases based on the same situations when the puppy owner decides to get a cat. The difference is in the characters, many temperaments create hot or mild atmosphere.
I would place a cat before the dog in the pack order because cats are more vulnerable against dogs. You tell your animals their place by treating them as number 1, 2, 3. Quite an interesting science "comparative psychology" suggests that for different species exists a common language, much of which existence you only can guess before told in words, though, progressing as an animal specialist, you may do your own discoveries. For instance: why a King would have his throne higher? Then, not difficult to guess why your dog wants to be on your sofa, and possibly, without you there. It works for felines as well, domestic cats are more social creatures than many think and can live in large groups, they fight for position too. By keeping your dog on the floor (ground level) and your cat on the sofa (above ground level) you already would determine your pack order. By the way - you should provide for your cat an escape route and a place, and possibly not one.
The most important resource is food. You can play here adjusting your pack order as much as you like, because there are breakfasts, dinners and suppers. Make your kitten hungry, stand against the wall, place a plate with cat food between your feet and let your cat eat. Let someone to bring your dog leashed in without a fuss, it could be better if nobody speaks. Feed and walk him well before training. Your dog would appear surprised first, then may try to come to you. Leash here only for emergency, the pup should be able to move freely. Ask him to sit and wait ( you command, your helper helps you manually). After 3-5 minutes of sitting down let the cat to finish the meal somewhere above the floor leaving on the floor a couple of bits for your pup to find. Your puppy should be in a sitting position when you are moving the cat on the window cell. Later, you can exercise your dog's patience by feeding your cat on the sofa. Never feed your puppy in presence of your cat until they have stable feeding habits, but that is a different topic.
You can tell your pup that the kitten is a pup by taking them together in the wild. Harnesses and leashes exist for cats too. Cat should not be frightened in a quiet area without people and other animals. Very often cats start running after dogs, probably, thinking that they are the dogs.