If a ResDiary Restaurant in your ecommerce platform isn't available to select when setting up restaurants for the Tables module, it is most likely due to the Restaurant in ResDiary not being set to work with the API.
To resolve this, you will need to contact ResDiary support (support@resdiary.com) and request that they set up the restaurant to work with the onejourney/JourneyTravel channel.
Only the ResDiary team can make this change.
Once set up correctly, the restaurant should be available for selection in the dropdown.