Sick betta

[Shearillusions]

Please help. Our betta fish got very sick n lethargic. Looked like he had a pimple on his tail. We did everything the fish guy said. Constant water changes . Medications and it was going away. We had a house fire n had to move now that we've moved his pimple has turned to a large cyst like white bumpy ulcer making a hole in his tail. It has developed to this point in a week. Looks sore and painful

 

[TNG]

That looks like a severe bacterial infection, so I'd provide treatment for bacterial infection. That said, it may now be too late for treatment given how severe it is.
Is the fish still eating? If not, it's humane to euthanise using clove oil.