A fact is something which is true. A theory is an unproven hypothesis which scientists propose as an explanation for something. Theories are tested by observation and repeatable experiments. Since no one but God observed creation and and creation is not something which is repeatable, no one can prove how the universe came into existence. Many, however, teach the theory of evolution as a fact instead of treating it as an unproven and unproven theory.
Christians teach creation as a fact because the Bible teaches it.
True science will not contradict what the Bible teaches. We can combat the theory of evolution by proclaiming what the Bible teaches and by encouraging unbiased scientific investigation and honest presentation of scientific facts. Honest science will not treat an unproven theory as a fact. The only thing that can convert a person to faith is the gospel. The goal of an evangelism presentation is always to present the gospel.