To find the changeset, navigate to the location on openstreetmap.org, right-click, query features, and select the feature in question. The web page should then look like this: https://www.openstreetmap.org/way/93668654/

In the left pane click "View history" to see all the changesets affecting that feature. Find the one you want, then click the link next to "Changeset #". The web page should then look like this: https://www.openstreetmap.org/changeset/104465654

The comment on the changeset might already contain enough information to answer why it undid your edit. If not, the left pane now has a text box for you to add a comment to the discussion. The user in question should receive a notification/email when you comment, and will hopefully engage in the discussion.

Sometimes one can find specific local communities here, too: https://openstreetmap.community/