You would need two apps for this edit.
Blender and VSCOcam.
1) In Blender, insert your background by inserting image on the bottom left square.
2) Next, insert your foreground by inserting image on the bottom right square.
This image is preferably your collar tag or the inner collar. You can take the photo of the collar with your shirt off also. Make sure the lighting is the same. You might want to avoid shadows also.
3)Once done, align both background and foreground accordingly to what you want.
In this example, both collar would have to be align.
4)After aligning, you will need to mask the foreground into the background.
Blender allows you to manually select what to mask by using your fingers. You may zoom in by pinching for tight spots.
5)If you are happy with your image you can blend it together and save to your album.
6)Finally, open the saved image in VSCOcam you may want to add fliters, adjust exposure and brightness and you are done!