All Web-apps, if not altered, will use the default User Agent String (Hana.)
To change this, click on the tab of the Web-app to be changed. Then select a new User Agent from those listed in the User Agent sub-menu of the Web-App menu.
That's it!
Alternatively, select Edit Web-app from the Web-App menu and then change it in the Edit sheet that opens.
For new Web-apps, there is a drop down list of available User Agents to select. Just choose and finish up.
If you do not see the User Agent String you want to use, read this topic on How to Add User Agent.