Any tips on how to potty train puppy from paper training?

Hi everyone,
We recently gained a new addition to our family a 4 month old mastiff pup called Alfie when we purchased Alfie the breeder had been paper training him which he continued to do when we brought him home 3 weeks ago, we couldn't take him out till wednesday just gone as he had his last injection the week before and the vet said we had to wait a week, we take him outside after every meal drink and nap we have placed one of his puppy pads with his urine scent in the corner of the garden to entice him to do his buisness but we can be outside for up to 40 minutes with him as soon as he comes back in he goes straight to his paper and does his buisness, we moved the papers by doing this he goes in his crate/bed and does it on his blankets,Im new to this and would love some advice,
thank you in advance

His crate should be made small enough to discourage emptying in the cage.
Take dog out on lead, do not wait forever. If nothing happens within a few mins, take back in side and put straight back in side.
Take some USED paper and place it in area you want the dog to eliminate in.

When the dog has emptied himself, give him a treat that he gets NOWHERE else.
do not chastise dog for emptying elsewhere, it will mean you need to supervise this pup very closely for a few days.

A dog may go out into its GARDEN before any injections have been given!