Put your fingers on the edge of the diamond in your ring and see if you are able to turn or move it slightly. Make sure to be gentle while trying to move the diamond, because if you do it harshly, then you will end up loosening the stone further. If the gemstone is sitting tight in the diamond ring setting, it means that it is not loose.
On the other hand, if the gemstone or diamond in your ring is slightly moving, then you need to get in touch with an expert jeweler and ask them to thoroughly examine the ring. In most cases, they will ask you to tighten the center stone in the diamond ring. However, if the prongs in the ring have worn out, you might not need to replace them too.