Welcome to the forum. As you are mid range of prediabetic then some modest changes to your diet should be all that is needed. One easy swap for cereals at breakfast is to have full fat Greek yoghurt with berries, seeds or nuts or a low sugar granola like M & S grain free fruit and nut only 9g carbs per 100g or other low sugar granolas which tend to be about 45-50g carbs per 100g as opposed to other cereals which can be as much as 70g carbs per 100g.
You may find this link of interest for some ideas for modifying your diet, it is based on a low carb approach of no more than 130g carbs per day (not just sugar)
https://lowcarbfreshwell.com/
Edited to add of course you need to look at the carbs in relation to the portion you actually have, with cereals it is easy to underestimate if you just eyeball the portion rather than weighing it.