There are two very significant scientific works, both are not easy to read or understand. They are The Theory of Relativity by Einstein, and A Short History of Time by Hawkins. If you study both works, you will realize that time is motion, and that motion is always forward. It never goes back!
But time can seem to go slower or faster, depending on travel. If, for instance, you travel by jet from New York to London, you are travelling faster than the Earth rotates. So you may arrive in London at the time before you took off in New York. You have "altered" time. But it is only an illusion, not a reality.You have only altered time relative to yourself; you have not altered time itself!