Convert Category to Tag-How do you undo it?

You can’t undo that conversion.

If you don’t have a backup from BEFORE the conversion, you will have to manually create those categories.

Check with your host, maybe they have a backup.

You could put your topic title in the search box… to find this:
https://www.ads-software.com/support/topic/140407?replies=6#post-672877

Note. It will work perfectly if you did NOT have tags before the conversion!

Oh, hadn’t seen that trick you pointed to moshu.

Can I suggest a database backup before doing that big of SQL.

I have a backup before the conversion but its didnt seem to restor the categories..maybe i did it wrong. i restored a week old backup and the categories were still gone

Then you did it wrong, sorry.

Did you do it as described here?
Restoring_Your_Database_From_Backup

hmm seems the backup plugin i was using failed to backup the category tables so im screwed. Im asking my web hosting company now.

Yes ive done that it restored the database but it seems my backup copies of the database are not complete due to some problem with the plugin:(