When we used to see the dog about to squat or half way through doing
the deed in the house, we always used to pick it up and take them
outside to the location where we wanted it to go to the toilet.

They soon got the idea of what had to be done.

We would say "No" when it tried to do something inside and when it did
do it outside it would get praised.

We used this method with all our family dogs but Lily the maltese
terrier was the hardest to train! As she got older she started going
outside thankfully although sometimes I still see little yellow patches
on my carpet at 3 years of age!! Grrr.

It's easier with a second dog so the second can learn from the first
but you obviously only have the one dog at this stage.

Good luck