First, make sure to save the agenda template you want to share.
1. Click “Tools” then "Template Library” in the left menu.
2. Click on the tab "Publish template".
3. Select "Publish" for the current template in the list.
4. Write title, description and set creator.
For privacy level, you can set "Private" (the template can be downloaded by all users in all boards you are part of) or "Hidden" (the template can be downloaded by only you in all boards you are part of). Then press "Publish."
Please just ignore the next step where the template can be shared with other users.
5. Switch to the other board where you want to download the template.
6. Click "Tools" then "Template Library" in the left menu. Go to the "Import Template" tab and then "Private/Hidden Templates". Click "Save" for the current template.
Now, the template is available to you (and other board users) when you need to create a new agenda.