@Ndayizeye
Check this link and translate - all in details explained:
If you have lost only one of the license plates, you must take it with you to the communication department when making a duplicate. After completing all formalities, it will be marked with a new homologation sticker.
It may also happen that the owner of the vehicle is a foreigner who does not have permanent residence in Poland. In this case, in addition to the above-mentioned documents, the communication department must also show:
passport,
a residence visa,
confirmation of temporary stay, temporary residence card or confirmation of temporary residence of the foreigner.
rankomat.pl/samochod/zgubienie-lub-kradziez-tablic-rejestracyjnych-auta-co-zrobic#:~:text=Je%C5%9Bli%20zgubi%C5%82e%C5%9B%20tylko%20jedn%C4%85%20z%20tablic%20rejestracyjnych%2C%20to,wszelkich%20formalno%C5%9Bci%20zostanie%20ona%20oznaczona%20now%C4%85%20naklejk%C4%85%20homologacyjn%C4%85.