There are many ways in which you can train a pet rat to become more trusting of your presence. We all know that they are naturally frightful animals, therefore, any of the ways are going to take some time and effort. However, this method seems to be the fastest and easiest way to gain their trust, if you stick to it. Having a neutral space is all you need, but you need to make sure that they cannot escape from the room. So, if you have a room that they stay in, with nothing that can hurt them, get in there with the rat. A bath lined with paper and with the plug in is a great place to do this if you do not have a dedicated room.
Move the rat to the area and out of the cage, as gently as possible. Then, all you need to do is sit with it and do not interact with them. You will need to sit with them a few times over the course of a couple of weeks and let them come to you. Maybe start by hanging your arm over the bath, but remember not to do it with any fast movements. Eventually, you will see that they start to come to you of their own accord. Move onto gently stroking them, and even handling them, as they become more trusting.