Can you have a resentment against yourself? Clearly, yes. On page 66, the Book refers to remorse, which is resentment against oneself.
Should you write about resentment against yourself? If there is an isolated resentment against oneself, one can usefully write about it as one would a resentment against anyone else.
If the resentment against oneself is general, free-floating, and volatile, writing is a waste of time. Maybe write out the second column, but the analysis in the third column and in the page 67 questions is so complex, covering as it does your whole life, it is beyond almost everyone, and does not yield any information that is not yielded anyway in the rest of the process. The process breaks down one's life problem into a series of discrete issues, situations, and areas, and this allows the individual to build up the jigsaw puzzle piece by piece rather than trying to paint the picture in one go.
What's the solution in that case?
Forgive oneself (same procedure as with others; see page 67).
Forgive others.
Make amends to others.
Be of service.
Accept what you can't change.
Change what you can.
One. Thing. At. A. Time.