I accidentally merged a branch and had "Push changes immediately" checked. Unfortunately I made a merge error and now I wan't to make a reverse commit to remove it. However every time I do it in SourceTree I get the following error:
error: Commit X is a merge but no -m option was given. fatal:
Found a good answer at last, it seems you need to use the terminal for this to work in SourceTree. This method is based on history deletion so not the best if others are also working on the project:
git push origin NAME_OF_BRANCH --forceinto terminal (you may need to enter your git repo username and password for it to accept the command)
If a message pops up later down the line asking if you would like to abort the rebase or continue. Click "continue". If you abort, the merge will appear on your local copy again.