Please tell us the exact model number (from the box or from the back of the set). Please also confirm that you're watching Freeview and not, for example, using Sky TV.
I've just wasted about a quarter of an hour looking through what Sony laughingly calls a 'Help Guide' (after having found that the PDF manual for the set contains no relevant information at all) and, as far as I can tell, your set doesn't have a 'reminder' function available. (Not all sets do. It's certainly something that I've never used on a TV).
https://www.sony.co.uk/electronics/support/televisions-projectors-lcd-tvs-android-/kd-55xg8096/manuals
Thank you so much. I used to use it as I didn't have catch up on my old TV so I just assumed they all had it .Just making sure I hadn't missed something .