From your inventory page, go into the More Actions button and from the drop down menu, select Upload Bundles
You will now be presented with the Upload Product Bundles pop-up. Upload the .csv file here.
Here is how the columns within your csv file will look:
Upload the file and select the marketplace you want to apply these updates on. Click the Update button.
NOTE:
If the Parent SKU already exists then it will be update
If the Parent SKU does not exist then it will be created and will be assigned to a new manifest.