If the Owner does not have an expense line item for their compensation, you must "pretend" that they do.
On the Expenses tab, we are attempting to view your business as a potential Buyer might - and determine the cash flow that the business would generate for that Buyer going forward. That means we need to look at the expenses as they are today (left side of the page), as well as what they might be for a potential Buyer (right side of the page; addbacks).
Even if you are a sole prop and your "compensation" is whatever is left over after expenses (i.e., net income), it's helpful to pretend that you are paid a W2-type income for the job you do. Consider what someone might be paid to perform the role and responsibilities that you do, and use that amount as the Owner W2.
This field should never be left blank and will typically be somewhere between $75,000 and $250,000.