Upload the updated nav.js first
Make sure you have uploaded the new nav.js file to your GitHub repository before following the steps below. That file is what actually creates the print button on every page.
Create the Workflow File
You are going to create one file inside your GitHub repository. GitHub will use it to update all your pages automatically.
Go to your GitHub repository
Open github.com and click on your Kingdom-Conversations repository.
Create a new folder called .github/workflows
Click the Add file button (top right area of your file list), then choose Create new file.
In the filename box at the top, type exactly this, including the dots and slashes:
Open the add-print-button.yml file I gave you
Open the file add-print-button.yml that I provided. Select all the text inside it and copy it.
Paste it into the GitHub editor
Click inside the large text area on GitHub (under where it says "Edit new file") and paste everything you just copied.
Save the file
Scroll down and click the green Commit changes button. Leave the message as-is and click Commit changes again to confirm.
Run It
Now you tell GitHub to go ahead and update all your pages.
Click the Actions tab
At the top of your repository page you will see tabs: Code · Issues · Pull requests · Actions. Click Actions.
Find "Add Print Button to All Pages"
You will see it listed on the left side. Click on it.
Click "Run workflow"
On the right side you will see a Run workflow button. Click it, then click the green Run workflow button that appears in the small dropdown.
Wait about 30 seconds
You will see a yellow circle: that means it is running. It turns green when it is done. If it turns red, come back and tell me and I will fix it.
Check your site
Visit any post page or series page on your live site, scroll to the top of the content, and you should see the small Print This Post button. That means it worked on every page.
That's everything ✦
Every page on your site, posts, series, doors, all of it, will have the print button. You never have to do this again, even when you add new pages in the future. Just run the workflow again and it will pick up any new pages.