Vanessa Van Edwards shares three ways to beat writer's block: skip the introduction and start with the section that excites you most, write the most compelling part first to find your flow, or draft your content as an email to the person you're trying to help.
Chapters
I recommend don't start at the start. I find starts incredibly paralyzing. The introduction of a book, it's like the hardest thing to write. The first few paragraphs of the book, do not start there. Like, you're not allowed. You should start with the thing you're most excited to write, whether that's going to be in chapter 20, doesn't matter. Start with the thing you're most excited to write because that's the energy that you need to get back into flow, and then your intro will come later, or your opening paragraph, or your opening page will come later. If those don't work, the last option is open up an email, pick the person that you're most trying to serve and help, and write it to them. Those three things I can usually through any writing doubt.