Have you looked at the anchored snapper?

@egomm Hi, thanks i will test with AnchoredSnapper.

The AnchoredSnapper that @egomm proposes works nicely if the vertices of both polygons are fairly close to each other.

The purple shape in your image looks as if it's an area that was drawn using arcs (1 point with a vector and curvature), which means that there might only be a few vertices that can be snapped. In that case you'd need to use an ArcStroker first on the purple polygon, which will get rid of the arcs and introduce more vertices.

Another option would be to use an AreaOnAreaOverlayer (and a Tester to remove the overlapping parts) in combination with a SliverRemover to get rid of the remaining holes.

Is it not simpler to just create a hull out of the pollygons (both together ).

Then cut this hull by the reference polygon.

Then clip the result by the (for instance) buffered edge of the target polygon.

And then lastly merge the target polygon with the clipped inside parts.

btw if you're gonna use snapping, then you might want to use it in segmentsnapping mode. ( sometimes you may need to use densifier for better result).

Try the SliverRemover. It will fill in the hole and assign the fill to either or both of the adjacent polygons - with various options as to which polygon it gets assigned to. It's a very good - and very little used - transformer.