Open the "Files" app. Usually this is built into iOS.  Once in Files, click the "Shared" tab, then click the three dots symbol in the upper corner. Click "Connect to Server"

Once you attempt a connection, it will have you "Connect As". Select "Registered User" if it is not already checked.

Name: AD\NetID
Password: Your Net ID password
Note* Substitute your Net ID for where it says NetID above.  Make sure to include the AD and backslash.