Our rescue had food issues and aggression was one of them. When I held him I would feed him until he figured out my hands gave food. I was eventually able to put my hand in his rush while he ate and give him food from my hand. It will take time but almost everything is possible.
When Chakka had her Anal glands removed there was a large wound with stitches at her butt.
We had to wash it 3 times a day.
I stuck her in the kitchen sink and ran warm water over her anus. With a soft cloth I wet and patted it to get all the poop and crusty blood off. She was fed treats as she stood there.
Thick baby wipes work well too...unscented