Lets keep this thread on topic please...
Looks like clamped fins to me, I don't really see a chunk, but there could be...
Clean water will help a lot with healing, there is no need for anything but clean water and maybe API Stresscoat.
Is there a strong current in the tank? Big finned bettas have troubles with the smallest current, try to baffle the flow from the filter to help it. Also is the tank cycled? There could be a small amount of a ammonia or something bothering him, test to make sure. If it isn't cycled you mentioned you had other tanks right? Get some filter media from those tanks and add a bit to his tank, this will speed the cycle up and will allow him to have a more safe level of parameters.
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