I tried to do this, so I could write you good instructions, and found that "Labels" isn't one of those fields you can auto set with a post transition on the Create screen! (That's how you'd do it for other standard fields and even custom fields via a plugin.)
Next, I did a quick Google search and found another Community post which seems to agree: you can't do it natively, but the plugin called "Script Runner for JIRA" might offer the ability.
Otherwise, this sounds like a feature request for Atlassian! You can log those at: https://jira.atlassian.com.
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Hi Community! My name is Amir and I’m on the Jira Service Desk product marketing team at Atlassian. Our team would love to understand how you’re leveraging our ecosystem for Jira Service Desk. Wha...
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