The title is pretty self explanatory.
Actually, you can. These are the steps -
1. Breed it with a Primarina that knows Sparkling Aria or and Freeze Dry.
2. Put the Gigantimax Lapras in the Nursery with 2 open moveslots, then put an offspring with Sparkling Aria and Freeze Dry and the moves will transfer over.
Alternatively, you could just breed a Lapras with those moves and give it a Max Soup.
Just watch, I am going to be sniped.