At the moment, there is only one way to change your profile cover photo and that's through the Personal Info tab of the Settings page.
Alternatively, you can access this by clicking on your profile photo on the lower left-hand side of the platform to open up additional menu items:
Click on Settings to open the Settings page:
The first tab will differ if you're a mentee or a mentor, but the Personal Info tab, where you can change your cover photo, will be the same for both. Scroll to the bottom of the Personal Info tab and you'll find the option to update your cover photo:
You can upload images of up to 1MB with a minimum dimension of 1440x1800. Clicking on the Change cover photo button will open a file selection modal which will allow you to select the cover photo you want to upload.