How do I access messages in icloud

You cannot directly access your Messages in iCloud. Messages are stored and encrypted in iCloud, with the sole purpose of synchronizing them between your Apple devices.

You can activate Messages in iCloud here:

Settings > Apple ID > iCloud > enable Messages.

If you have messages in iCloud, they will be synchronized on your Apple device.

You can read more about Messages in iCloud here:

Set up iCloud for Messages on all your devices - Apple Support