To proxy into a user's account, locate their account, and from the account details page, click on ‘Login as User’. 

Note: Please be careful when in proxy mode. Proxy mode should be reserved only for verifying course statuses. We do NOT want to make account changes or launch courses from within proxy mode.

This warning displays after you click on 'Login as User': 

'Clicking OK will log you in as the currently selected user. Any changes you make will be made as if the user themselves made the change.'