It would help if you posted what you’ve done.
In general the approach is:
- create a myopenhab.org account
- install the openHAB Cloud Connector add-on
- configure your myopenhab.org account with the secret and UUID as described add-on
- verify that myopenhab.org shows your instance is online
- Navigate to the Items you want to be accessible in Google Assistant in MainUI and add the appropriate Google Assistant Item Metadata to the Items.
- In the Google Home app add the openHAB account.
- Ask GA to “sync my devices”.
You must complete steps 1-5 before step 6 and 7. If you do not have any Items configured with GA metadata prior to linking the account and syncing devices, the sync will fail.