SolarWinds support assisted me with creating a rule which monitors a particular OU. However, I would like to modify the rule. When I attempt to do this, I have no options to choose another OU. Not too sure how to do this.
Okay, this is a little vague, so a screenshot of the rule you're editing would help.
However, I'm seeing two possibilities:
If it's the former, I'm betting you'd have just edited the text. If it's the latter, you need to go to Build --> Groups and add a new Directory Service Group. This will pull in SECURITY GROUPS ONLY, though an OU can also be a Security Group. Once it's added, you'll be able to see it in the Rules editor under the "Directory Service Groups" drawer.