For each library you exported create an empty folder on the new computer, probably following the same structure. I have my libraries like so:
Code:
D:
Calibre
Libraries
Books
Covid
Default
...
Test
So I would recreate that structure on the new computer.
The folder you Exported to (e.g. F:\CalData) should contain files named part-0001.calibre-data, part-0002.calibre-data…. part-nnnn.calibre-data.
When you Import, first thing is to browse to and select the folder you Exported to: e.g. F:\CalData.
Then for each library you exported, you will be prompted to browse to and select the empty folder you just created for that library.
BR