置之不理 is a four-character idiom (成语) meaning 'to completely ignore or pay no attention to someone or something'. It often implies deliberate neglect — you know about the matter but choose not to deal with it. The structure 'place it and not manage it' gives the sense of setting something aside and refusing to engage. You can use it with 对 (duì) to specify the target: 对…置之不理.