Unless things have changed, it’s the ancient and tedious drill of moving the data from the Primary to a new field with a duplicate, and moving the other data to the Primary with a copy-paste.
Before you do this make sure any formulas or other dependencies on the existing columns are well known and can be migrated or updated.
also before you do this make a duplicate of your table, as a backup to revert to in case things go awry.
Duplicate the Carrier field, making sure the option Duplicate cells is on. Title the new version Carrier (new).
Change the name of the original Carrier field to Pickup Date (new).
Convert Pickup Date (new) to a Date field type, configured exactly the same as the original Pickup Date field. (This will also wipe the text content of the original Carrier field so first make sure that field copy went well!(
Copy the data from the original Pickup Date to Pickup Date (new) by these steps:
Making sure there’s no filtering going on, select all the cells in the original Pickup Date field column by first clicking once on that field’s Row 1 cell to select it. Scrolling all the way to the bottom of the table. While holding Shift, click on the last row’s cell once.
Copy to the clipboard (CMD-C on Mac, CTRL-C on Windows).
Go to the top cell in Pickup Date (new) and paste (CMD-V on Mac, CTRL-V on Windows). You should have two identical fields now.
Recreate/update any dependencies or formulas pointing to the new columns.
Delete the original, now unneeded Pickup Date field/column.