Unfortunately, this doesn’t guarantee that you’ll capture the Ultra Beast. If you miss the Pokémon, you’ll have to defeat it in another raid for another chance to capture it.
If you’re confused about raids, you can check out our guide on how to battle in them.
Beyond this, though, there aren’t any other ways to capture Ultra Beasts; battling them successfully in raids will reward only the most dedicated trainers with an Ultra Beast to add to their team.
Source: https://www.distractify.com/p/how-to-catch-guzzlord-pokemon-go