Copy files like PANTONE+ Solid Coated.acb to a thumb drive or cloud storage.
The primary way to get Pantone colors back into Illustrator is through the official plugin: download pantone colors for illustrator link
If you obtained a legitimate .ase file (e.g., from a client or past project): Copy files like PANTONE+ Solid Coated
This is the required method for the most current color data. download pantone colors for illustrator link