Time Machine
How do I transfer my Time Machine backup to a new hard disk?
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There are many many articles that explain how to do this including:
https://www.howtogeek.com/335090/how-to-migrate-a-time-machine-backup-to-another-drive/
I assume that you are moving your existing Time Machine to a higher capacity and newer External Hard Disk. If that is not what you are intending to do, please let us know.