If you are the membership owner, simply log into the app with the account that has your Peloton Bike membership. You will gain access to the app at no additional cost as long as you continue to have an active Peloton membership.
If you are not the membership owner, the membership owner will have to add you to their membership. This can be done in a few ways:
On the Peloton Bike, you’ll need to be added as a rider.
On the Peloton iOS app, have the membership holder log in. Once logged in, you can go to the More tab → My Subscriptions → Select the Peloton Subscription you would like to add to → Click “Add Account” → Enter your username and tap "Add Account".