Hi @MRConcept! Welcome back to the community. 
This should be fairly straightforward to accomplish, though the details depend a bit on the exact nature of your workflow logic. I've put together a really basic example below:
The next step is to trigger this workflow from within your app:
By chaining on an Event handler, we're able to take the response and update the value of the text field.
I hope this explanation helps! Let me know if you have any additional questions. 