What would be a good topic to write about on the idea of collaborating with a group of people with beliefs that differ from mine, but then my initial feeings were changed over time?
There is no way that anyone who does not know you can tell you what topic to pick. We do not know when you have worked with a group whose opinions or beliefs have differed from your own. Therefore, we cannot tell you what to write about. What we can do is to give a few suggestions.
First, think about times when you have worked in groups. This could be for an instance in which you had to work in group for an assignment at school. It could be something as simple as a class discussion that has changed your mind about an issue. Another possibility is that you were a member of a sports team and had differences with others about how to play or about your feelings towards a coach or a teammate. Another possibility would be if you belong to any groups such as a church group. You might have had disagreements within that group. You will need to think about your own life and try to identify possible instances to write about.
Second, once you have something to write about, you should be sure to discuss why you changed your opinion. You should think about what other people did that caused you to change. Was there, for example, any way in which they acted that made you more receptive to listening to them? It would be good for you to reflect on their actions or words so as to think about what it is that allows you change your mind.