Hi, I am not sure what you mean by merge 2 applications, but you make use of the copy-paste feature in the builders to copy elements or sections of your forms or userviews from one to another.
You can also retain the apps separately and share data between the apps just by referring to the same form data tables. This might be a suitable way to structure your apps too in many cases, sometimes having smaller apps makes it more manageable compared to a very large single app.