How can disable create pull request on create step?

I want to validation sourceBranch and targetBranch with my condition that declared in my bitbucket plugin and if condition false dont get create pull request.
I read bitbucket documentation and find topic about “Repository Hooks and Merge Checks Guide”
https://developer.atlassian.com/server/bitbucket/how-tos/hooks-merge-checks-guide/
But i want to disable pull request on create step.