To filter the object records, files, or attachments using Advanced Search SOQL on the basis of Created Date, you need to put the date in the following format - YYYY-MM-DDThh:mm:ssZ, Below are a few examples for your reference - 


1- Object Record's:  If you want to fetch the Object record's values that were created before 1st May 2023, so the query will be CreatedDate <= 2023-05-01T00:00:00Z



2- Attachments: To filter the attachments' records, you need to put a query like CreatedDate <= 2023-05-01T00:00:00Z on the following box as shown below - 

3- Files: To filter the files' records, you need to put a query like ContentDocument.CreatedDate <= 2023-05-01T00:00:00Z on the following box as shown below -