Paying tax to the tax office

Hello and nice day, As in the topic, I got a car borrowed from my grandpa from Poland. I will probably drive it next 2 years with it here. From a known I have heard that there is a possibility to pay a voluntary tax, my place of residence is in Germany and the car is registered on my grandpa in Poland so is not my car. So so that I could not have any bad thoughts I want to pay for the car here tax so not bumbling With this question I’m going to contact you. P.s. I’ve called a contact person of an insurance form he has informed me that I can drive with the vehicle here and every time there will be a check, always say that my grandpa is visiting. MfG enkelinho