The quickest way to translate an NCS colour reference to RAL, if you have a sample of the NCS colour, is to use a RAL Color Reader this will measure any sample target and give the closest RAL number.
An alternative is to do a visual check of the NCS colours in the NCS Index against one of the RAL books – the RAL Design system is likely to have the closest match as RAL Classic colours are more vibrant.
Or you can Order a Colour conversion from NCS Colour in Sweden (they will check visually) https://ncscolour.com/product/colour-translation-notation-to-notation/.