This wikiHow teaches you how to add your Microsoft OneDrive account to the Files app on your iPhone or iPad. To do this, you must first update your iPhone or iPad to iOS 11 or later.
Steps

Step 1. Open OneDrive

Tap the OneDrive app icon. This looks like a white cloud on a blue background.
If you don't already have the Microsoft OneDrive app on your device, you can first download it from the App Store

Step 2. Login to OneDrive
Login with your OneDrive account email address and password.
If you're already logged in, you can just wait for the OneDrive app to finish loading

Step 3. Close OneDrive
Press the home button below your device's screen to minimize the OneDrive app.

Step 4. Open the Files app on your device

Tap the large blue folder icon on one of your screens to open the Files app.

Step 5. Tap on the Browse tab
This tab can be found at the bottom right of the screen.

Step 6. Tap on OneDrive
This will open OneDrive in the Files app.
- If your Cloud accounts cannot be found on this screen, you must first click 'Locations' at the top of the screen.
- Optionally, click 'New location' if OneDrive is not in the list. Then tap the OneDrive slider on 'on'