What Souffle said. Please separate them immediately. Syrians should never live together, only solitary. You can sometimes see if a hamster is female by the shape of their back end (viewed from above when they are standing on all fours, not upside down). A male tends to have an elongated back end. A female is more of a rounded back end. Although again maybe difficult to tell with a long haired hamster. You will find out in 16 days if he/she is pregnant.
But do please separate them immediately. Or they will kill each other. I would also write to the pet shop and formally advise them that Syrian hamsters should not be sold as pairs who can live together, and quite an animal health charity on that.
This article has some helpful info
Can Hamsters be Kept Together? — Hamster Society (Singapore)
More here
Syrian Hamster – National Hamster Council
Everything you read will say Syrian hamsters MUST live alone.