When shoul you train abs when doing Push Pull Legs?

My work out routine usually looks like this Monday: push Tuesday: pull Wednesday: 2.5km swim Thursday: legs Friday:2.5km swim Saturday: 12km run Sunday: rest

So my question is, where should I add the abs/core exercises? I know visible abs also depend on diet but there are a lot of benefits to having a strong core so I wanted to get that working before going on a cut. Where should I add them? What exercises should I do? Thanks to everyone in advance