If someone knows for a fact that you have Monero and they know the exact amount, and want to know where it came from:
- Move them to a new wallet
- I mined these coins a very long time ago, I do not have the mining equipment anymore
- Also the wallet I used to mine them was on an old computer that got infected so I moved all to this new wallet
If someone suspects that you have Monero but does NOT know how much:
- Imagine you own $10k in Monero
- Move a small amount to a wallet ($200??)
- If authorities ask you how much you have, show them the wallet with $200.
- Go back to scenario 1 (I got those 200 from mining a long time ago etc etc)
If no one suspects that you have Monero, and for now you are "in the clear":
- Follow good opsec
- Do not tell anyone that you have Monero
- Do not exchange that Monero for fiat using KYC services. Always use something like Haveno, or use the Monero to buy prepaid cards anonymously to use in shops
- If someone starts suspecting that you might be using Monero but does not know how much, revert to scenario 2

Of course it is better if you avoid anyone knowing you have Monero altogether.

Remember that you always have the option of moving them to a new wallet, say you got hacked and have no access to it.

Of course all this depends on your country and how authorities are there. If you live in a very authoritarian area where authorities do not care about evidence and they only care that "you look guilty", nothing will save you. If you live in a country where you must go to court and be proven guilty, I think with Monero its pretty easy to do any of those steps and cover your ass.

But as always, try to not be discovered using Monero in the first place