The home page content is in src/WebForms/WebApp/Default.aspx - here’s an updated file you can use:
Copy the new file over the original:
cp labs/appservice/lab/Default.aspx src/WebForms/WebApp/
Commit the changes:
git add src/WebForms/WebApp/Default.aspx
git commit -m 'Homepage update'
And push to your remote:
git push webapp main
You’ll see the build output again, and the new content should be live in a minute or two.