Help with making course meet requirements for screen readers

I'm new to Articulate and online course development and wanted to tap into the wisdom and experience of others.

We're developing and module and one of the requirements is that it meets accessibility requirements for screen readers. I've looked at tutorials 71/72 and it looks like we have to add alternate text to be picked up by a screen reader. Have I interpreted this correctly or is there a magic button I can press to automatically add this function to the course?

The free reading software I was trying to test it out seems to be a little bit selective in that sometimes it works fine and other times it doesn't seem to pick up the text, even though I haven't done anything differently. Does anyone have any experience or tips that they would be willing to share and/or any suggestions for free screen reader software you've used to test things??

thanks.