It may be best if you ring the VW dealer and explain that you have a motability SEAT and see what they say.
If you do want to do it yourself B&Q do it for £11.99 but wear old clothes and shoes and if you spill it on the floor wash it off immediately, it dries as a white crust, also be aware that after top up the car will take time and a few miles to register the addition of the adblue.
Daughters motability car Hyundai Tucson Ultimate self charging hybrid Serenity White Moss Grey interior.
My car SEAT Ibiza SE Tec 1.2 petrol TSI 2017.