I was checking out the migration documentation, however, I'm not sure if I overlooked or it's not stated, but I noticed that the documentation only explains how to add column, what if I want to remove a column?
In the Migrations section of the Realm Swift documentation, it actually shows you how to remove two columns (firstName and lastName), and replace them with a single new property (i.e. fullName).
To remove columns from your Realm file, all you need to do is remove those properties from your model object, and then run a migration.
If there's information in those columns you wish to keep, you can choose to move that information to a new property inside the migration closure (Which is what the documentation demonstrates). This is completely optional, and if you run the migration with an empty closure, then the columns will simply be removed and the data deleted.