To use the way you have described you would have to create a relationship field and link on every single item that points back to your "Template Instructions" app item allowing it to pull those instructions over.
A much easier approach (in my opinion) would simply be a calculated field in the app template of each app called "Instructions App A" or whatever.
In this instructions field you can meet podio's requirement of using a referenced field value by typing @Unique ID and selecting that variable (it will appear blue)
Then follow this with two forward slashes //
Lastly, Open a quote " and type out whatever instructions you would like for that app, close with the end quote "
Attached is a pic of this applied
The tiny bit of code you see of + "\n" + is telling the system to make a line break between the numbered steps in the example.
Using this approach, it will appear as text, only editable by those that have Admin access to open and modify the template of the app, and it will not require you to set up related fields to the instructions on each and every item.