Don’t punish your dog if they pee inside. Regardless of all those old training ideas punishment isn’t a good deterrent for house training. Yelling at your dog after the fact just confuses them and makes them nervous around you. If you catch your did in the act you can try to get their attention & move them outdoors. If you’re successful & they continue going once you get outside praise them like crazy.
The process is the exactly same for older dogs as it is for puppies; prevent accidents from happening by using baby gates and a crate if possible, create a predictable schedule, learn to recognize your dog’s potty signals, accompany your dog outside and immediately reward for all outdoor elimination, properly clean any accidents and supervise your dog until you’re sure that he understands the rules.