How do I give access to the website to a co-worker?

You can use the Collaborators feature to give multi-access to the website, it allows to add co-workers and provide them with full or limited access to the website:

Note that the feature is paid. To view prices and buy the option for working together, go to the Site Settings → Collaborators → click on the Pay and manage button.

To edit your website, a collaborator will be enough to have a free account.

The maximum number of collaborators is 25. You can assign one or several projects to a collaborator.

You can find the full guide on configuring at link: https://help.tilda.cc/multi-user-access