Adding additional file(s) to currently opened layers

[SpartaPhoto]

 If I open a couple of  files grouped together in Affinity for layering work there are times when I need to add an additional file(s) of the same image to the other layered images currently opened up in Affinity. Being a new user to Affinity this seems to be more difficult than I imagined. Can someone enlighten me on how to do this.  Thanks

[firstdefence]

Welcome to the forum, 

To add an image to an existing image already open, you can use File > Place or, you can simply drag an image into an open image, both will generate a new layer with additional image.