Just pick one Quad in the UV Editor and Select one Edge and Align Auto and then do the same for the other three Edges (or, use SHIFT+R to repeat the last Operation, so: Select one Edge and Align Auto, Select the next Edge and SHIFT+R and the next Edge, SHIFT+R,…) until all Edges (of that Quad) are aligned to either X or Y and you have a perfect rectangle. Select that rectangle and CTRL+L to select the whole Island (what is connected to that Face in the UV Editor) and Uv > Unwrap > Follow Active Quads (it’s only one Active Quad, so I don’t know what that ending s is doing there). Done
