Please follow the below steps to delete it from DB:

• Use browser developer tools and try to inspect the content of the Data transform/When rule that is opened,
• Place the mouse pointer as shown in the attachment to find the respective pzharnessv2_ruleformXXX css file name,
• Try to get the record in pr_sysgen_static_content table using below query or similar to your database,

          select * from pegarules.pr_sysgen_static_content where pyfilename like 'pzharnessv2_ruleform%' and pyfiletype = 'css';

• Delete the respective record from the table.