PowerApps SharePoint Update Tutorial

I have a canvas app in PowerApps that writes to an existing SharePoint Online list. Each list item is uniquely identified by a combination of “Date” and “User name.”
Now I need a clear, working example that lets me locate an existing item with that composite key and update two fields—“Action Item” and “Created Time Out”—using a single button or form submission.

Scope of work
• Walk me through the exact formula or Patch statement that finds the record by Date + User name.
• Show how to embed conditional logic so the update fires only when specific criteria are true (e.g., a status toggle or checkbox).
• Demonstrate the solution live (screenshare or short video is fine) and supply the finished code snippet so I can paste it into my app.
• Provide a brief written step-by-step guide so I can replicate the setup in future screens or lists.

I’m comfortable adjusting minor details myself; what I need is a concise, reliable pattern that fits the above list structure and works inside the current PowerApps/SharePoint environment.