Setting multiple SKUs under a main parent SKU

[GasCityScrubs]

I recently uploaded two full brands worth of SKUs into my system but now I need to nest a lot of SKUs under other SKUs for variants.
All the SKUs imported have the attributes already set up, and they are simple products.
Is there a way to batch add these SKUs under a parent without setting them each individually?
I know you can go into the parent and select attributes, create variants and link them one by one, but that would take me months.
Is there a solution to do this in bulk using product numbers or something?

[Benjamin]

The best way is to export the SKU list, add the main SKU and attributes, and import the file back.

[GasCityScrubs]

How do I set a specific SKU as the main SKU? All the attributes are set already, as are the product numbers and all the matching information

[Benjamin]

If you use the template here https://support.woopos.com/knowledge-base/importing-a-sku-list-with-excel/
The first column is the main SKU. The second column is the variation SKU.