When you insert a storage card that has not been used on HTC One M9 before, the card will be mounted as removable storage by default.
If the storage card is new or doesn't have content you want to keep, you can format the storage card to use it as internal storage for HTC One M9
Home screen, tap
- Under Removable storage, tap the storage card name.
- Tap .
- Tap Format as internal.
- Tap Erase & format.
- Tap Format.
- Follow the onscreen instructions to move your installed apps and their data from the phone storage to the storage card.