If you have been vaccinated in a non-EU country then you can convert your foreign proof of vaccination to a Dutch certificate which you can upload to the CoronaCheck app (the Dutch Digital Corona Certificate (DCC)). Note that both your jabs need to be done using a vaccine that has been authorised by the European Medicines Agency (EMA), otherwise you cannot receive a DCC in the CoronaCheck app.
You can call the following number to schedule an appointment: +31 (0)30 800 2899
Visit this page for more information on the conversion process and conditions for conversion. (English)