This option is available on Matching Column (Step 2) of Update, Add & Export feed only. This field have extra setting.
There are a few settings for this field which are:
1. Weight Unit
If you want to set any unit to the weight value in the store such as "no changes", "kg", "g", "lb", and "oz".
For example, if you updated your product's weight as 5 and your feed file does not have the unit for this field. You can select it here to add the unit to it.
2. Weight Converter
Weight converter is the changes you can make in your weight of products. There are a few selections for the converter.
For example, if the weight of the product is using 500g which is known as a gram then you could change it to 0.5kg which is known as a kilogram.
3. Weight Delimiter
Weight Delimiter is provided in the weight field which has two options Comma and Decimal Point. You can choose any of them for your products.
If you don't have a column as a weight field in the feed file, you can set the default value as you need for all the products. You need to select the option as static and enter the value you want to set it as. This will be the example of set all the weight to 0 value.