Just go through all objects, BBCode objects have an icon with two blue brackets - [ ]
If the project is very large and you can't find them, there is a trick. Add a new BBCode Text object, name it ABC123 for example. Then create a family and add ABC123 object to it. The list on the left will show all other objects of the same type.
Then replace them manually with Text objects one by one. After that you'll be able to switch to runtime 3 and enjoy all the new features of Construct 3.