How can I add another admin to a team when I am not the owner?

I am org owner.
My ex-colleague, an org admin, created their own team and added me to the team as an admin.
They have now left our organisation and I’m trying to add their replacement in but I don’t get drop downs allowing me to change their status from member (student) to admin.

  • What will happen if I delete the ex-colleague from the organisation? Will the students’ work and team be maintained?
  • Is there any way to add in an additional admin without the use of the team owner?
  • How do you transfer ownership of teams?