How long is the layover?

I would suggest you to take the bus called "airport bus service" that runs between both airports, if you are by youself, otherwise, would recommend taking a uber (Black, if you have lugagge with you). The ride between airports should take 90 minutes by bus, and I recommend AT LEAST 5 hours to do so (immigration, picking up the lugagge, customs, buying tickets for the bus, waiting for the next bus, eventual traffic, check in at CGH, security, etc...).

I strongly recommend that you don't use public transportation, as CGH is really poorly served by it.