Hi Freerk,
thanks so much for helping and supporting us!
The easiest and most forward way would be to open the Dutch PO translation file under wp-content/themes/bricks/languages with a free software like Poedit , make the changes and when finished, send it to us via email to help@bricksbuilder.io.
Poedit is a simple to use, but yet powerful tool.
Again, thank you very much for your help 
Best regards,
timmse