When plugging in a disk to your Mac, you may find it showing up as uninitialized in Disk Utility, and can't be mounted at all. Once the storage device becomes uninitialized on Mac, you can't access tons of stored data. Therefore, you ought to use iBoysoft Data Recovery Software to grab the Time Machine data before fixing the uninitialized hard drive.
Read this article "Fix Uninitialized Disk on Mac Without Losing Data" to know how to recover the uninitialized Time Machine backup drive with iBoysoft Data Recovery Software.