Before adding fish urinate in the pond a few times, wait 1 week. Or add ammonia from the drug store.
If you already have fish they will provide the ammonia.
The bacteria are already in your pond, them just need food to reproduce.
Whatever method is used you measure high ammonia, then falling ammonia, followed by high nitrite and falling nitrite. When ammonia and nitrite are back to zero you bio filter is seeded.
If you already have fish and you measure zero ammonia and nitrite your bio filter is already seeded and there's nothing to do.