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.
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.