Hi
Good luck with you new housemate. Kudos for the rescue as well!
I have trained many pups and the method I use isn't a new one, but it seems to work well.
First, a small crate is a big help for those times you can't be with your dog, most dogs won't eliminate where they sleep.
I choose a place, or places, For the pads where the dog has eliminated ( had an accident) before,
I put the clean pad, face down, on a fresh pee spot, step on it, and turn it face up. It may sound gross, but your dogs scent on the pad really helps.
Dont be too fast to change the pad if you can tolerate a bit of pee on the pad. I even have left the pad down after a BM ( after removing the solid waste of course) . Dogs are so scent driven that, in my experience, these icky steps really seem to speed up that Aha moment.
I am also a beliver in positive reinforcement and treat training.
Shaping behavior ( small correct steps toward the main goal) helps. In other words, praise and treat even if your dog just gets really really close to the pad. Use it as a chance to get the urine scent on the nearest pad.
Keep your cool and stay calm and positive, your dog will get the idea.
I would also keep taking your little one outside, even if it is cold, especially if your dog is well trained to eliminate outside..
Good luck!
Starr