I see the white lump and it could be a number of things, the least likely being a 'tumour'.
If it is a tumour, ie cancerous, then salt or medication is unlikely to have any effect and, when a genuine tumour is identified, then veterinary surgery is usually involved to remove it. This is obviously going to be expensive and every good vet will weigh up the benefit of surgery, compared with the stress caused to the fish.
That said, stressed fish are prone to bacteria and viruses and, seeing the environment you've placed the fish in, I suggest you look up some more resources of Better Betta care.
Here is just one of many.
KGTropicals Betta Care
Whilst I'm sure your heart is in the right place, please resist trying to play Fish Doctor. There's a multitude of many diseases, illnesses and parasites that can trouble fish and these are usually tricky to diagnose correctly, especially when you're new to the hobby. Whilst some conditions can be treated with shop-bought medications, many of these can be harmful to fish and so your diagnosis has to be correct. Most conditions can be treated without cost...
Stress is THE most common cause of seemingly poorly fish and so properly maintaining an appropriate tank will keep the fish stress-free and healthy.
Please remember that healthy does not just mean disease or sickness-free...it means that the fish is also 'happy' and thriving. This means that the fish is behaving as it should in the quality wild.