If the internal storage is damaged, then the only way to fix it is to either have the storage replaced, or get a new device.
Unless the damage is to software rather than hardware. Then you can try doing a "Hard Reset" of the device to see if it will help.
NOTE: Doing this will clear 'all' the data on your phone, so it is suggested you not choose this option unless you have to, or aren't worried about losing anything on the phone.
Be sure you back up any data you want to keep, to a computer or cloud account, before doing the reset.
To "Hard Reset" the phone...
1. Make sure that the phone is actually powered off.
2. Remove your SD card, if there is one in the device.
3. Press the "Power" and the "Volume Up" buttons, together...