Masking Basics - Please Help

[cluelessn00b]

Still learning, and I know what I want to do, but I don't even know how to search for/ask for it. (I'm using Affinity Designer for Mac Desktop)

All I want to do is:

I have a background layer with some images on it. Let's call it B1

I then pasted a smaller image on top. This image has a face, and then flowing hair (black color) and is surrounded by white border. Let's call it F1.

All I want to do is make remove all the white from the foreground image so that it's just the face/hair showing on the background. I know how to add a mask layer to F1, and then use an eraser to wipe as much of the surrounding of the face - but it isn't perfect because it's really hard to clear out the fine spaces between hair etc. 

Is there a way I can erase by color - so for e.g. can I choose "white" and remove all white color from the foreground image so that it's just the image i want showing up on the background.

I don't even know if I explained it right but please help. I think it's a simple ask... but who knows

[Pšenda]

4 hours ago, cluelessn00b said:

remove all the white

In APhoto is Erase White Paper, try Flood Fill Tool in Pixel Persona.