First Passport for Mac full, so bought new one an backed up to it. Now old one will not show up on MacBook. Please help!

I have had a 1T Passport for Mac that I use daily. This morning Time Machine said I had no room left and I need a new external device. I bought a 2T MY Passport. I plugged it in and it formatted and Time Machine did a complete back up. Now when I go to plug in the first passport (1T), it will not show up on my MacBook. It is absolutely running, but Mac is not finding it. What did I do?? Can someone please help? Flipping out here. Everything is backed up to that 1T one.
Any advice or help would be greatly appreciated!

Hi tjonc,

You can have a look on below article in this concern.

I think your drive must be there in the Disk Utility. However,

  1. Disconnect all external drives from your MacBook

  2. Restart Mac

  3. Go to Time Machine via System Preferences.

  4. Click Select Disk button

  5. Select the current Time Machine device and press Remove Disk button

  6. Now connect your old 1T drive to Mac

Wait till the drive appears on the Desktop or Finder. Let me know if this worked for you.