I apologize for the delay! Thank you for your question.
That's great that you wrote about "Plan". "Act" really is just putting the "Plan" into action. You may find some insights in the Strategic and Action Planning sections of the toolbox here. Basically, Act happens when partners follow through on their commitments to take action - usually these steps are outlined in your action plan. An action plan tells you who will do what by when.
I'll also point you to the Developing Interventions toolkit because interventions are one way that partners take action. So this section can provide some examples of how actions are selected and carried out. This section includes barriers to action which is important to consider when you are planning for or while you are in the "Act" phase.
Finally, I would recommend the Advocating for Change toolkit, as advocacy is another way that groups take action and there is a section outlining an advocacy action campaign.
Wishing you the best on your research project and thanks again for reaching out with your question!