dodge and burn with neutral grey overlay layer

[gram tot]

I am use to accomplishing dodge and burn by using an overlay filter layer filled with neutral grey and then painting with black or white to dodge and burn.  I am new to Affinity.  I have created the layer.  (New Fill Layer; neutral grey; as an overlay filter.)  How do I make sure I have a white or black brush?  I can see something happening on the layer, but it does not change the background image.  Can someone walk me through loading the brush with black and white since I may be doing that incorrectly?  Also, what I am doing wrong that the background image is not changing?  

[MEB]

Hello gram tot

Welcome to Affinity Forums  :)

Create a new layer then go to Edit ▸ Fill..., set it to 50% grey, and change the Layer Blend mode to Overlay in the Layers panel.

Use the Paintbrush Tool to paint in this layer with black/white (you can select its colour from the Colour panel on the top right of the interface). You can swap between the two pressing X.

Check the context toolbar (right above the work area) for more brush options.

[gram tot]

Thanks.  I've got it working correctly now.