Raise the temps to 83 degrees and add 1 tsp of AQ salt for every 5 gallons, read the instructions because memory fails me lol I personally would put the fish into a bare bottomed container for his treatment as this will be easier for 100% daily water changes
This is something I posted a few days ago on another thread similar
I would recommend putting your betta in a bare bottomed quarantine tank, this will be easier to do 100% daily water changes. The tank should also have aeration,ick is known to attach itself to fish gills making it difficult for them to breath and as cooler water has more oxygen than warm this is essential when raising the water temps. Add about 1 teaspoon of aquarium salt per gallon of water and change the water 100% daily adding the same amount of aquarium salt each time, you should continue the treatment for a week and if the ich is still present visit your LFS for an anti ich medication.
You should also carry out a 50% water change on his main home, cleaning the decorations and gravel, If I am wrong someone is bound to correct me, so stay tuned for people with more experience than me