If you are wanting to change your password -- log out of Covidence and do so at either the Covidence sign in page, or the Cochrane sign in page, depending on where you normally log in. You might find it useful to check this video here.
If you want to change the email address that is associated with your account -- login and hover over your initials in the top right hand corner. A drop down menu will appear. Under your email address click on "PROFILE" from which you can edit your personal details, as shown in this video here.