Welcome to the forum.
A prediabetes diagnosis will mean you have an HbA1C of between 42mmol/mol and 47mmol/mol (48 being the threshold that puts someone in the diabetes zone) and is an average of your blood glucose over the previous 3 months. As you say it is a wake up call to do something about it. How much work you need to do depends where you sit in the range.
As it is all carbohydrates which convert to glucose then reducing your intake and losing weight if you need to will all help to bring your level down.
You may only need to make some modest changes by cutting out some of the big hitters like cakes, biscuits, and sugary drinks including fruit juices and reducing portion size of others like potatoes, rice, pasta, bread, breakfast cereals, tropical fruits and having meals based on meat, fish, vegetables, eggs, cheese and fruits like berries.
Looking at packets or Google search for FOOD X total carbs will give you the information to make better food choices.
Many people find a low carb normal fat approach successful that being less than 130g per day but there are other way you will also see mention of here. Reducing carbs gradually is better as it is gentler on your eyes and nerves.
This link may have some ideas that will help you with food choices, and a few do's and don'ts.
https://lowcarbfreshwell.co.uk/