Thank you for your follow up.
Your friend will have couple of option to recover his personal belongings from his ex.
The first thing your friend can do is to report the fact that his belongings have been taken by the ex without his permission to the police. While police will take a report, there is a possibility that police would not want to get involved in this situation, given the domestic nature of the relationship your friend and his ex were involved in, prior to the ex taking the personal belongings of your friend.
If the police would not further investigate this situation due to its domestic nature, then your friend will have to file a lawsuit in the local small claims
court to gain access to the storage and to recover his possessions
Unfortunately, those would be the only two options for your friend to pursue this matter either criminal or civilly or both, since the storage is in the ex's name only, your friend will not be able to get access to it without either ex's consent, or criminal / civil court order.
I wish you and your friend all the best!