It would be helpful if Platform Managers could manage all other users' lists. For example, after an employee leaves and they are no longer employed, if the Platform Manager forgets to impersonate them and clean up their lists before they are no longer employed, it's impossible to manage those lists unless the user account is assigned permissions again.
You can. Go to Manage Lists > List Admin, and select the name of the list's original creator from the dropdown. Next click the 'User Access' link, search for your name, and add yourself. Then change the radio button to 'Copy' (it defaults to 'Run').