The first thing I want to say is that there is no requirement that trademarks must be registered in our country, which means that whether you register or not has no direct relationship with whether you use it or not. You can use it without registering. But when using it, be sure to check whether the trademark you are using has been registered by others. If it is registered, you are infringing it.

To the question of whether it infringes "Rieter Express", the answer is no, because he has not successfully registered it. If he has successfully registered it, you may infringe it. If they register it and then stop using it, it’s fine. They have no right to pursue the ones you used before. Besides, there is another possibility that their “Rieter Express” is not registered. It’s also possible that the “Rieter Express” you apply for later is successfully registered. Possibly, because it has the word "express" in it, there may be more risks.