Svn – How to change svn working copy between two different repositories

Or do I somehow use the month old backup recreate the svn repository. So that I have some history and lose history only for the last month. Not sure if this possible, but if it is please list the steps.

That's the approach I would recommend. You'll be left with a repository that has all of the old history, and a single big commit that has the sum of all changes that occurred in the last month.

1. Recover your backup from a month ago and set up your subversion server again.
2. Check out a working copy from this recovered server. The contents will (obviously) be a month old. (We'll call this WC1)
3. Go to one of the working copies that you had checked out from before your lost your server... the one that is most up to date. (We'll call this WC2)
4. Manually move the files from your most recent working copy (WC2) into their corresponding location in WC1. Don't move directories, just files. If directories have been created, make them again using svn mkdir. If files have moved, move them with svn mv. In this step, you're essentially manually recreating the difference between your month-old backup, and your most recent working copy.
5. When you think you've got it, use svn diff to double- and triple-check the giant commit.
6. Commit the changes
7. Delete the broken working copy, as all of the changes in it have been migrated back into the subversion repository on the server.

I have a wrong entry on the authz file (it was trying to give permission to a deleted group), so I deleted the entry and it's working now