The first thing I would do when troubleshooting is gaining as much information as possible and going from there. Knowing what exactly the issue could be affecting can help to know what steps to take. Learning more about the issue can come from testing the device and asking the user good, clear questions so that they can give information on what they have experienced on their device.
After using this information critically, this should narrow down what the cause could be. From there, I would make a plan and complete the steps of that plan. After taking these steps, I would make sure that the problem has been fixed by running some tests. If it has not been fixed, I would go through the information again and take similar steps to find another solution. If it has been fixed, then I would let the user know what happened and how to prevent the issue in the future, and I would document the issue and what fixed it to keep a record of it.