When an external hard drive is damaged there are times when it can be repaired changing the device's internal hard drive. It may also be that the internal disk of the same works correctly and can be used.
In both cases you have to disassemble the enclosure and internal controller to access the internal disk and separate it from the other components of the device.
Here you have a collection of videos showing how to unmount an external hard drive, classified by manufacturer. All videos are available on YouTube and are the property of their respective authors.