Check out the solution in the video (ETL) Violation of PRIMARY KEY constraint 'PK_Constraint' - Different Source and Destination Keys. One pattern I've seen quite often is developers changing primary keys or sometimes swapping primary keys from source to destination. While there may be some legitimate contexts to doing this, be extra careful, as we see an example in the video of this.
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An hour of thoughtful planning can be worth a full work week. Planning isn't sitting in a meeting and discussing things. Planning is considering what you will do, what the effects are along with what the limitations of what you're capable of doing. If changes need to made to the primary key, then you should plan this change and recognize the effects that it will have.