Hello, did the Sony camera change it? or was it with some general repairer of cell phones? In any case you should have returned the equipment verifying the correct functioning of the new camera, I am not an expert in hardware but I think the change did not work, let's move on to the following: You comment that you can not find the icon to turn camera, this happens to you only with the camera application or with any application? Try to check that it works in another application such as whatsapp, at the moment press send photo brings an own icon to use front camera, if it does not work then they definitely did not make the change well and it would be best to return with those who did the work to fix it (or do your job well: P). If it works well in another application then probably the camera application is damaged, you can do 2 things:
1. Try another camera application, in play store there are many options.
2. Reinstall the entire operating system of the cell phone but not with PC Companion of Sony but with Flashtools, this application brings everything you need to do it, even with the latest versions you can find the most appropriate firms for your model.