Unf*ck aligns vertices along an implicit spline curve. This is especially useful in situations were the Bevel tool overshoots vertex positions.
Edge loop of at least 4 edges.
The best way to select them is by using the Pick Shortest Path tool via
Ctrl + Select Mouse.
f*cked up geometry
Note, that the 2 vertices at the end of the selected edges will not be changed, they are only used internally to setup the implicit spline curve.