Log in to your Appstore connect Account (https://appstoreconnect.apple.com/login) using your Apple ID and the associated password: 

Select the option "My Apps" on the Landing page to open an overview of the existing App entries for the App store connect Account:  

Click on the App entry that should recieve the update, to open the information panels (for example Yumpu APPKiosk Test)  

Select the App entry via the "App Store" -> "IOS-App" tab:

Look to the information panel on the right side and scroll down until the "Build" entry is visible:  

Copy the information shown right next to your App icon in to your App information of your Yumpu Useraccount. In the example shown the Yumpu Appkiosk Test app has been uploaded with the Version 1.01 and the build number (1.1)