You will need to feed a few wild bacteria an ammonia source so they multiply into two large colonies. It takes at least 4 weeks often longer.
Only a test kit will tell you if the bacteria numbers are large enough to consume a daily dose of ammonia equal to the daily poop load of the projected stocking numbers.
Shops sell bottles of what they say are the bacteria. Bacteria need oxygen, warmth and old poop ( ammonia) Ask yourself if a bottle sitting on the shelf has any of the requirements to survive?
The bacteria we all use are everywhere in small numbers. I suggest you would be wasting your money buying it.
You may be able to buy bottled ammonia In your country . If not you can add a half a dead prawn/ ( king prawn) and yes let it rot in the tank.
Alternatively you can add dry fish food and wait till that goes rotten, adding more every day.
Even if you have a full working nitrogen cycle it is recommended to only stock part of the final number of fish at one time..