Gridlock

I have the comicbook toolkit you wouldn´t happen to have a youtube video or another step by step tutorial on how to do it?

How do i create this kind of effect inside the letters? I know how to create dots but i can´t seem to create the same effects as shown in the picture. Where the dots are small on the top and big in the bottom. So how do i create it? It should be said i am very much a noob when it comes to Affinity Photo so as detailed of an explanation as possible would be great.