I want to upgrade my MacBook Pro 128 memory

You cannot upgrade the storage (or RAM) on a 2019 MacBook Pro. The SSD is soldered to the logic board.

You can add external storage by connecting an external drive or network attached storage device.

You'll have to tell us what model/year MacBook Pro. Some can be upgraded some can't.

Older MBPs can have storage upgraded, newer ones have the SSD soldered to the logic board and cannot be upgraded. Apple menu > About this Mac, what model/year is yours?