If you 3d print for any length of time, things will eventually start to get loose. One of the things that people often have questions about is how to tighten up the print head. It’s a pretty straightforward process, once you know how it’s put together. The roller bearings that most manufacturers use have an off-center hole. This is done intentionally, so that the bearing can be rotated to tighten or loosen. 

The process is to loosen the bearing(s) slightly, then rotate it until you have a snug fit between it and the rail that it rides on. Then tighten it back up. I typically check my bearings for fit when there is a significant weather change, when I have a crash, or if something just feels “off.”