merged two branches, and pushed, how to backout/strip?

[Uwe Brauer]

Hi

I merged a feature branch into default and pushed. I shouldn't have
done. If that were a private repo, I would strip and that it is, but now
how I am supposed to clean up the mess, the graph looks basically like
this:

@    changeset:   143:ec02f4c5e97e
|\   tag:         tip
| |  parent:      138:7e1a64287b87
| |  parent:      142:1dd731cf6a6a
| |  user:        Uwe Brauer <oub at mat.ucm.es>
| |  date:        Sun Jan 08 19:42:20 2017 +0000
| |  summary:     Merged
| |
| o  changeset:   142:1dd731cf6a6a
| |  branch:      vs-11.89
| |  user:        Uwe Brauer <oub at mat.ucm.es>
| |  date:        Sun Jan 08 09:57:53 2017 +0000
| |  summary:     Update Makefile and style/*.el

143:ec02f4c5e97e is the unwanted merge. I tried to rebase, but this was
of course refused.

I might update to the last commit in the default branch, add stuff
commit and push creating a new head, but are there better solutions?

Thanks

Uwe Brauer