You need to use Date Token Calculator to get the target date 30 days ago.  Then use Search Repository and plug the date token into your advanced search syntax to 30+ day old documents in your target folder.  Then, because you will have multiple results, you will need to use a For Each Entry loop to Delete Entry.

The search syntax will look something like this where {%(DateTokenCalculator_30 days ago) is the token you created with the Date Token Calculator.

{LF:LOOKIN="\IT\Testing\oldies"} & {LF:Created<"%(DateTokenCalculator_30 days ago)"}