Introducing a new animal, be it a dog or a cat is always a very delicate time, especially in the case of having to introduce the new animal to another that can hurt him, so before attempting any approach, make sure that your large dog will not try to eat the cat, okay?
If this is already a well-resolved subject and you want to continue with the presentation, always try to do it calmly and gradually, for example, it would be very interesting if they could see themselves through a glass door or a gate, where you will be able to observe the reaction of both the dog and the cat, as the cat in fear tries to attack the dog and even the person holding it.
Go doing this exposure several times a day, for short periods and several days in a row, always rewarding both for the desirable behaviors they may have. As the days go by, we can let them smell, if they touch …
A cool tip is to put one on each side of the door or gate to eat close to each other and in that way, they associate the presence of the other with a pleasant experience.
When they can smell and touch without stress, you can try to put them together in the same environment and see how they react to each other. But always stay close if anything goes out of control. Thus, they will become friends or at least accept the fact that they will have to live under the same roof.