[Plugin: WooCommerce] Merge products to variations

I have a customer who has added his products in the following way:

– product a (print 1)
– product a (print 2)
– product a (print 3)
– product b (print 1)
– product b (print 2)

Is there an easy way to merge products to variations of a product? In order to create a structure like:

– product a
– print 1
– print 2
– print 3
– product b
– print 1
– print 2

Thanks in advance!