Firstly they need to prove that the Earth is as old as they say it is and they need to demonstrate this through the scientific method, not just make a flat bald-faced assertion that it is 6,000 to 10,000 years based on the Bible which is half-arsed circular reasoning.
Second, remember you're arguing with creationists - people who think there's a supernatural omnipotent, omnipresent, omniscient deity that is alpha and omega, the beginning and the end, the outside of time creator yet simultaneously they can't accept the Earth is far older than previously thought. Creationists don't care for the abundance of evidence around them, learning about the natural science, dating technologies, or the Hypothetico-deductive model to verify observable data - they only care about their subjective religious world view about reality, which is why their bullshit shouldn't be taken seriously and NEVER taught in schools.
Second, remember you're arguing with creationists - people who think there's a supernatural omnipotent, omnipresent, omniscient deity that is alpha and omega, the beginning and the end, the outside of time creator yet simultaneously they can't accept the Earth is far older than previously thought. Creationists don't care for the abundance of evidence around them, learning about the natural science, dating technologies, or the Hypothetico-deductive model to verify observable data - they only care about their subjective religious world view about reality, which is why their bullshit shouldn't be taken seriously and NEVER taught in schools.