As long as your router wasn't used by Noah on the ark, it will almost certainly have a button labelled 'WPS'. (It might possibly, as on my own router, be dual-purpose and be labelled something like 'WPS/Reset'). Start by finding out where it is.
Then follow the instructions here:
https://www.epson.co.uk/viewcon/corporatesite/products/mainunits/faq/8026/15963
(NB: When you press the WPS button on your router, you might need to hold it in for just a second or two. Don't press it for too long though if it's marked 'WPS/Reset', as keeping it pressed in for 10 seconds will reset your router completely, leaving you unable to connect to the internet. I made that mistake recently!)