I wouldn’t recommend the method shown in that link 
. Too messy, overly difficult, and too much potential to damage the chip accidentally. If you do want to disable the contactless feature of your card (which I wouldn’t now recommend, despite having done it myself!), see an earlier post of mine (click the down arrow at top left to see the image of my card):
https://community.monzo.com/t/disabling-contactless-feature-on-card/8130/52?u=jzw95