I don’t know about Macs. find the equivelint of Disk Management in Windows and see if it is recognized there. If so maybe TestDisk http://www.cgsecurity.org/wiki/TestDisk will fix partition structure if it’s corrupt
Hi tere, Go to Disk Utility and verify if the drive is not being recognized, try running FirstAid on the drive to repair it and if it cannot be repaired you might need to partition the drive. If it does not show in Disk Utilities, please try a different computer and let me know the outcome.