13 Spark coolant

Doing all the PM’s on dads 13 Spark with 144k, he got it 79k 5+ years ago. It should have Dexcool in it but as you can see it has the green stuff. He’s never had it changed and not seeing it on the receipts. Debating if I should do flush with distilled and at least running the yellow stuff from OReillys or Dexcool. OR just drop what’s in it and put green back. He doesn’t drive 60 miles a day since he retired and it rarely gets driven.. we might end up with it eventually.