If you want to use the ZipRecruiter integration on more than one job board, you'll have to first set up the integration for a single job board following the steps in this article.
Once that setup is completed, you can enable ZipRecruiter on additional job boards. The two setup processes are very similar, but any other job boards won't require you to confirm your setup before enabling the integration.
To enable the integration, navigate to a job board and edit it. (Configure > Job Board & Posts > Ellipses next to job board > Edit Board Settings)
Scroll down to the Allow candidates to apply directly from ZipRecruiter section and click Yes.
Scroll to the bottom of the settings page and click Save.