How to undo Mark goal run as ignored in Eclipse build in Eclipse preferences?

m2e uses a file YOUR_WORKSPACE/.metadata/.plugins/org2.eclipse.m2e.core/lifecycle-mapping-metadata.xml to store the global lifecycle mappings.

You could manually open this file and remove the corresponding entries. After that you should reload the global lifecycle mappings using the 'reload workspace lifecycle mappings metadata' in window > preferences > maven > lifecycle mappings. But you could also edit the file while Eclipse isn't running. In this case you don't have to reload anything.

If you have only added one ignore then you can delete the file completely (maybe make a backup somewhere just to be safe). If you want to remove one but leave the others then take everything between <pluginExecution> and </pluginExecution> for your choice.

I hope this helps a bit. :)