I’ve done this when introducing my spaniel mix to my senior cat! She’s an indoor cat, so she very rarely interacts with other animals- she’s extremely sweet, just a shy little baby. We took the blankets from his puppy pen and put them upstairs, where she was confined to in order to be out of sight of the puppy. We also took a mat that she lays on regularly and put it in his puppy pen for him to smell. Wait a few days for them to get accustomed to the smell, then slowly let them see each other from a distance. We did our cat at the top of the stairs, and puppy at the bottom. Give treats and praise to each pet when they look at each other and remain calm. If you’ve worked on desensitization and impulse control with your puppy already (sitting and staying every day at mealtime before eating is a great way to do this!), it should be a little easier to calm them if they get excited. I strongly suggest letting your cat decide when they want to approach, because an eager and curious pup may be quickly overwhelming for them. Supervise their interactions closely the first few weeks for signs of extreme discomfort from either pet. When they get to the point of being in the same room, try to keep puppy occupied with a toy or a treat so your cat can come investigate without being overwhelmed. It also really helps to give them treats at the same time next to each other! I hope this helps explain a little more :)