Ill tell you something about ammonia and your ammonia test. The ammonia being picked up by your ammonia test might not be all that harmful.
Most ammonia tests arent testing for free ammonia, they test for total ammonia nitrogen. This is free ammonia PLUS ammonium. While free ammonia is extremely harmful in even very small amounts, ammonium is nowhere near as harmful. The proportion of free ammonia to ammonium you have picked up in your test is determined by your pH and water temperature. The higher the pH and temperature, the more ammonia will be present compared to ammonium as a proportion of the 2. At typical aquarium temperatures you need a very high pH before 0.5ppm total ammonia nitrogen becomes harmful to your fish.
Picture attached, green is good, yellow is start to take action, red is take immediate measures.
While seeing ammonia in your test is a sign that something has happened its not something to panic about. 0.5ppm is what you typically cycle a tank at and is relatively safe.
Are you sure your cycle crashed? Maybe something died and you had a sudden increase in ammonia that your cycle needs a little extra time to process out?
If your cycle has crashed then proceed as you would a fish in cycle. Water changes to keep ammonia + nitrite combined below 0.5ppm. Feed lightly. Introduce some established media if you can, bottled bacteria if you cant.