Open a web browser and go to iCloud.com
Sign in with your Apple ID
Select Messages if it appears in your iCloud apps
Open the conversation you want to view
If Messages is not available on iCloud.com, use a Mac with Messages in iCloud enabled
Open the Messages app on the Mac
Sign in with the same Apple ID
Turn on Messages in iCloud in Messages settings if needed
Wait for messages to sync
Open the conversation to view your messages
On iPhone or iPad, open Settings
Tap your name
Tap iCloud
Tap Show All or Apps Using iCloud
Turn on Messages
Open the Messages app to view synced messages