Need toolkit to reestablish connection of my external HDD (no recognizable volumes) to MAC. Seagate Toolkit unavailable in APP store and my App Store preferences will not allow mw to open Toolkit provided by Seagate.
Earlier Mac models
when you use software from just about any manufacturer for their storage device you run the risk of that same software not being compatible with macOS updates / upgrades. it can cause the software to stop working. at best this will cause you a headache. at worst it can render your data inaccessible. it is always best to use disk utility to erase and format a drive before use to remove any preloaded software.
since you are using such software, i think your options are somewhat limited.
you may want to contact seagate and see if there is an update for their software.
alternatively, if you have a backup you can revert your macOS to the version of macOS that the drive was working on and transfer your data to another storage device and then erase and format the seagate device before putting it back into service.
Erase and reformat a storage device in Disk Utility on Mac - Apple Support
Seagate Toolkit download problem
