I developed a novel technique (from 2016 until my graduation in August 2019) in my area of study as a PhD student. I transferred the technique to another PhD student, which took all of Fall 2018. Today I found that the second student and my (ex)advisor submitted a paper in July (before my graduation), and neither included me as co-author (even though I helped the second student adapt my technique to his problem with significant hand-holding), nor cited my papers documenting the technique.
Today my (ex)advisor sent an email asking me to help transfer my technique to a third student. The third student informed me that the second student (who left the research group for another) is not cooperating, and stalling with excuses of other commitments. Of late, my (ex)advisor has become very toxic to work with, and has lost numerous good grants. What do you advise I do in such a situation?