First step (essentially always): comment on the changeset. Politely point out that you object and ask them to join the discussion here if there is no agreement.
As to the matter at hand a achavi link or similar so that we can actually judge the effrcts would be good.
Simon
On 27 June 2022 11:38:15 CEST, RB tanrub@gmail.com wrote:
A user is destroying precise landuse mapping in Wallis. "Simplifying" in this case turns precise landuse cover into weird angles and destroys the work done by the previous contributors while harming the OSM database. Such moves could furthermore clearly be perceived as aggressive. Typical examples of the vandalism can be observed there https://www.openstreetmap.org/way/965324922/history#map=19/46.02973/7.11287
What is the appropriate way to react to such attacks against the project?