Answer: People who are against immigration may fear the loss of jobs, increased tax burden, or just don't want to encounter "foreign" culture or language. People for immigration usually value the skills or labor that the immigrants bring. They see opportunity to provide housing and other needs that will bring economic benefit.
Explanation: Changing people's minds isn't easy. It may be helpful to listen to their reasons for their opinions, and acknowledge whatever is valid. Then offer examples and facts that support the alternative points of view. There may be ideas they haven't considered before. Learn from the discussion. It goes both ways. Specific situations are likely to have different solutions.
It may be helpful to recall that most Americans are descended from immigrants. Many blessings and many problems have resulted from the introduction of the laws, culture, science, traditions and invasive species (germs, plants, animals etc.) that were not native to this continent.