To change the scratch disk assignment
Choose Edit > Preferences > Plug‑ins & Scratch Disks (Windows) or
Photoshop > Preferences > Plug‑ins & Scratch Disks (Mac OS).
Choose the desired disks from the menus.
You can assign up to four scratch disks of any size that your file system supports.
Click OK.
Restart Photoshop for the change to take effect.
Good Luk.
Wood