A few options. Cover the entire lawn for an extended period of time with a bunch of tarps or cardboard so no sunlight reaches the grass. Kill the entire thing. Start over with native seeds. Or roto till the entire thing
For me personally Bermuda grass never stood a chance against all the clover, dandelions, cheeseweed, purslane, tall flatsedge, and broadleaf plantain that make up a lot of what used to be the lawn. Some of those are invasive technically but at least rabbits come to eat the dandelions and plantains