Let me get this straight: you have Bitcoin at one address and you want to take away your own ability to spend it? Because a watch-only address as far as I know is an address that is not yours and you import it to monitor activity.

If that's the case, I guess the best way would be to create another wallet without that address and import it as watch-only but ultimately you would be able to spend it.

It would be nice if you could explain why you want to do this as an internet search indicates it is used as a scam:

https://medium.com/blockchain/the-truth-about-watch-only-addresses-c9708b5b892

https://www.reddit.com/r/Bitcoin/comments/21jh2i/attention_blockchaininfo_people_are_scamming/

What do you mean by "watch-only addresses"? When you generate your wallet from seed you are generating an HD wallet from seeds, meaning you can generate multiple addresses/private keys from those seeds, and when you export your master public key you get the view wallet file.

You can list and track multiple master public key using third-party applications (bitcoin trackers^[1][2]) and these applications also allow you to list individual addresses.

watch only wallet is useful in tracking your coins and cannot be used to prove anything, because the proof requires signing a message, which requires a private key.

[1] https://CoinTracker.io
[2] https://coinstats.app/