Hi Kimberley 

Thanks for posting your question in the Community! To create a corporate template where the template is accessible in your team's template drop down menu you must be on an enterprise account and be assigned as a Team or Template Admin role. If you aren't able to access this option it's likely that you aren't assigned as a Team or Template Admin and I recommend reaching out to your account owner. For more information about this feature please review this Help Center article.

As a workaround you can also create a custom template and then share it with team members by using the typical share features for a document. Your team members can make a copy of the document to create their own document from your template. 

Let us know if you have any additional questions!