It's not possible, sorry. However, there are two ways to get Alolan Marowak in Sword and Shield.
You can transfer one from the Gen 7 games if you have a subscription to both Pokemon Bank and HOME.
The second way is in the Isle of Armor. Talk to the Diglett hiker, and recover his lost Digletts. Finding fifty lost Digletts will make him give you an Alolan Marowak.
Source: Experience and this
Hope I helped!