Hi,
Puppies need to be deworm in 5, 8 and 12 months of age. After this every 3 months.
If you don’t see worms in the faeces, it doesn’t mean that your dog is free from intestinal parasites.
You can buy wormer from your vet (I don’t recommend buy from pet shop, because not every wormers working properly).
Because your puppy wasn’t deworm yet, I recommend give him wormer now and after 3 weeks again, than every 3 months (ask your vet about correct dose).
Sometimes you can buy from pet shop Panacur Small Animal Oral Suspension 10% (without prescription – is very good).
If you will buy this wormer, you can give to your dog 0.5ml for 1 kg body weight for 3 consecutive days, after 3 weeks this same dose (0.5ml for 1 kg body weight for 3 consecutive days).
After 3 months you can buy Panacur granules 4.5g (1 sachet for 10 kg body weight one time) or Panacur Small Animal Oral Suspension 10% 1ml for 1 kg body weight one time, and this same every 3 months.