There is no set in stone method to dry hopping but here are a few tips based on what I've seen with Spike equipment
1) Quick access through the 4" lid port. Remove the cap and drop in your hops and re-attach the lid. If you want to do a quick purge of Carbon Dioxide, feel free to attach the gas manifold to the blow off port and apply 5 PSI and purge air from the pressure release valve.
2) Nylon bag is recommended, it helps keep the beer clean and you can tie it to the cooling coil if you have one! Flowers, pellets or leaf hops may be thrown in without the bag per the users discretion.
3) If garlic/hay flavors develop, it might be from oxidation. Try dry hopping earlier, even during primary activity. That way oxygen is readily absorbed by yeast and displaced with CO2. Also, use fresh hops! Check the date on them. Yeast can mingle with hop flavors in a way that you've probably tasted in NEIPA. So that is another element of adding them earlier. You'll have to play with the strains of yeast and hops as well to see what works best!
4) 5-7 days is usually enough on a hop. You can do two sessions as well. One early and one late to add a different dimension to it. Experiment!