I have this dumb cane that I bought 6 months ago from a local store. It did not grow much since then, may be 2 leaves. The existing leaves are also turning brown and are curled up. I also saw something like fungus few weeks ago. So I sprayed some water mixed with baking soda. I water it once a week and it is placed near a window (but not too close). I thought it might be overwatering that's causing browning and inhibiting growth. So I repotted it using store bought potting soil. I washed the roots thoroughly before repotting. What else could I do in order to make it a healthy plant.
You probably were overwatering it. You have already done way more than you needed to do. Just let it get settled in its new pot. Only water it when the top 1-2" depth of soil is dry. Never water on a schedule. Plants will dry out at different times, based on many environmental factors.
Assuming it is winter, you should not next expect it to be growing. Indoor plants in winter are in a semi-dormant state. They are still growing, but much much slower. Since they are growing slower they need much less water. So it is important to only water when the plant needs water.
I caution making anymore changes. I also caution you spraying anything on your plant, unless you know what the problem is. The wrong spray can make things much worse.
The only other advice is to give it a bright window. They like very bright, but indirect or diffused light.
What kind of water are you using? These browning margins and tips are indicative of high salts building up in your soil.
Don't water until your plant/pot/soil feels light when you pick them up. If you are on city water that would be a very good reason the tips are turning brown. The water is full of salts
What do you do for fertilizer? Another salt source.
You could take your plant into the shower and turn on the cold water. Soak your plant (s) turn the water off and allow them to drain well. Don't use saucers for this drenching.
Pick up your plant and its pot and feel the heft of your plant with soaked soil. You'll be able to tell clearly your plant needs water. Do not water until that potted plant feels very light. Just do not water.
Otherwise, your plant looks healthy other than too much water, the soil stays wet too long and the salts will continue to brown the margins and tips.
For better drainage, put some broken pieces of tile beneath the pot and above the saucer.