Combining SKUs into one listing?

I have like 20+ SKUS that are all in separate listings. I was wondering if somehow I could combine these SKUs into one listing (they’re all the same product just different designs). Like one listing with 19 variations. So that when someone clicks on one listings they automatically see everything else I have listed as variations. Do I have to delete everything and relist as one SKU w/ 19 variations or is there a way to this post-publishing? Thanks!