Cannot delete data source or knowledge base

Hi! I am trying to shut down my Amazon Bedrock, but the issue is that there is one knowledge base that I cannot delete. When I try to change data deletion policy of that knowledge base's data source from DELETE to RETAIN, I get the following error:

undefined The role with name AmazonBedrockExecutionRoleForKnowledgeBase_d2j7q cannot be found.

I may have deleted this policy prior to deleting the knowledge base. How can I resolve this issue and delete the knowledge base successfully?

Thanks in advance!