Your poor fish looks really stressed
It almost looks like the fish is injured to me? or some kind of genetic defect?
With ammonia/nitrIte problems you are looking for red/brownish colored gills and either the fish will be grasping at the top for air or lying still on the bottom.
If you don't have any live plants I would get some, hornwort is great for sucking out the bad stuff because it grows very fast and is easy to grow and inexpensive.
As for the water changes I would probably try and do 20% every other day, the problem is that they more water you change the more it could slow down your cycle but if you don't change it enough the fish will perish.
Do you have a testing kit?
When I was cycling I would test for Ammonia and nitrIte everyday and change 10 to 20% of the water if the ammonia was over .50 and the nitrite was over 1ppm. (sometimes it was daily and sometimes every 3 days depending on the readings from the test kit). Don't worry about your nitrAtes right now, you want those in your tank.
Aquarium salt can help with nitrite levels but it won't help with the live plants and I think in your position the live plants might help cycle the tank faster and will be more of a benefit to the fish.
Do you understand how a tank cycles? I am sure there is tonnes of info on the forum if you look around, it really helps to understand how the cycle works and what your water tests mean.