Which sponsors are displayed in the mobile app and on the event depends on their sponsorship package - you can set those properties when you are creating sponsorship packages.
You do not need to take any additional action in order for sponsors to appear in the mobile app. As soon as a valid contract is concluded with a sponsorship package, they will automatically be displayed in the app.
To show sponsors on the website, some work is required. You will need to talk to your webmasters and ask them to include the sponsors widget on your website where sponsor logos should appear.
You can easily get the widget code by going to your event home, then selecting "Event Settings", "Widgets and Links," and searching for the "Sponsors Widget". Use that code to display the sponsors widget on your event’s website. There are numerous optional parameters for that widget, which are all described on that page. Be sure to read through all the options and configure the widget in the best way suitable for your website.