You can export the variation related fields and edit them in the bulk file.
Here are the steps:
1- Select the products and go to Export>Custom…
2- Select the fields from the Variations section.
3- Download the file from the “Notifications” from the top right.
These are the fields in the file.
IMPORTANT NOTE: If you want to create a parent-child relationship, you must copy the parent sku into the parent_sku columns of the child products.
IMPORTAN NOTE: If you set up the variation types as “color,size”, you must fill the variation options column of the products in an order. (first color, second size)
IMPORTANT NOTE: If you want to delete a specific field data, you must leave the cells as empty. This action will delete the data which you have already in SA, when you upload the file back into SA.
4- After the changes, upload the file back into SA.