I'm not sure I can really help you the way this question is currently worded because I'm not sure what you need and what you're trying to do. Some questions I have for you -- if you can answer these, I (or someone else) would be more likely to be able to give you good help.
By prologue, do you mean an introduction to an essay?
What do you mean by "going to freedom?" Do you mean escaping from slavery?
What are you trying to do in this essay? Are you supposed to be giving facts about something? Explaining something?
In order to help you write an introduction (if that's really what you want) it would be very helpful to know answers to these questions.
You can answer here, or you can message me.
If the prologue is supposed to establish an exposition for a narrative about enslaved individuals envisioning freedom, I would suggest that some research on the topic might help. Reading portions of The Autobiography of Frederick Douglass might assist you in this setting. Douglass lucidly recounts what it is to be a slave and how freedom is perceived from the lenses of bondage. Perhaps, appropriating some of these ideas in your prologue might add credence to it. Equiano's descriptions of life aboard the Middle Passage might be another source to assist you. In order to articulate the vision of a slave's freedom, one has to pay due diligence to the life of enslavement and be willing to engage in as much detail as possible about what it means to live as a slave. Certainly, Equiano can provide evidence to that end. I think that the most important element in any writing of a slave narrative is credibility and authenticity because of the reality of the experience which is at stake. Being able to absorb the feel and timbre of works which can operate as primary sources can assist.
Equaino should suffice as an example and a general central topic of your essay.