Thank you for contacting us.
You need simply copy short description and paste it in main description field in Mass Product Changer, if you want to use one short description for multiple products.
Let us know if any other questions occur!
all short descriptions are different so, can i copy 500 records at a time
Thank you for reply.
Unfortunately, this operation can not be performed via Mass Product Changer. Please, try to reimport products using Modify only method.