What the primary teacher needs to do

Go to the course you want to share with a co-teacher, then select Members on the left. Then select the Add Members button.
​

Here you can manually search for your co-teacher or just scroll the list to find them. Once you select all the teachers you want to add to the course select the Add Members button at the bottom
​

In the Members list click the cog on the right of your co-teacher and select Make Admin in the drop-down list.
​

It will prompt you with a confirmation step, click Confirm to complete the co-teacher process.
​