Once you open the bag, it's recommended to add Prime to neutralize any ammonia present - just dilute in some tankwater first
I use a 5in1 test strip to quickly compare bag vs tank water (or enquire of shop) ... if pH, GH, KH are similar, I just net & add to tank as this is much less stressful than the "fish in a bag" scenario
Note that before adding new fish (I'm assuming you don't have a quarantine tank)
- 50% water change
- lights off
- reduced CO2
Drip acclimation should be done with aeration & very dim lighting, also avoid vibration/looming shadow stress - floating plant etc cover is helpful
If new fish arrive in stressed condition, I leave lights & CO2 off at least 1-2 days (assuming there's sufficient ambient light to observe new fish)
If there are dead/nearly dead fish in the bag, best action is to remove fish from that environs as soon as possible
Again if I know the water conditions of the shipping agent, I'll have prepped some tap water to match
If fish water condition is unknown, I'll still pour off fish into net & add to a clean bucket etc with tank water & Prime, then add air stone etc
Worry about separating out dead fish after
Then consider if these fish are best kept isolated or added to (community) tank