How can I add a new variant after importing products in Shopify?

Hello! when importing from Aliexpress, sometimes all the variants comes under colour or something similar.

for exampel: you got 3 blacks, those three blacks have 1, 2, 3, 4 meters.

They are all come under colour and nothing under the length. when trying to fix this in shopify by adding a variant, it just give duplicaded empty products ( Like this ->> https://ibb.co/6rm7s40 ) that i have no clue what do with. Why not just let us add a new variant so we can move it. its so badly done in Shopify i wanna just try another platform.

Or did they create an app to make it more easy with a monthly plan? Cuz i know they could fix this in a heartbeat if they wanted too.

is there an easy way to add an variant after importing to Shopify?