Hey! So, I did a google search and can't find a specific tutorial, but the way it's done is by utilizing headings and heading sizes as well as regular paragraphs. This appoints different levels of importance to screenreaders and gives it structure for what order to read it in. Basically, chapter/section titles get Heading 1. Smaller sections within a chapter get Heading 2. Bodies of text within those are paragraphs. If everything is assigned a structure like this, when you export as a tagged PDF, it's ready to go. If you hop into the discord for the Jam, I'd be happy to hop in video sometime and do a tutorial for you OR male a screenshot/written tutorial in there. That's a bit hard to do here on itch.
Here's the discord invite. https://discord.gg/5RPTesND
If you don't have discord, I'd be happy to chat in Twitter dms or whatever works for you!