Were you told what your HbA1C was that gave you the prediabetic diagnosis as depending on how close you are to the threshold of over 47mmol/mol that will indicate how much you will need to do. It is basically a wake up call to make some changes to your diet and try to get a bit more exercise if you can, losing weight if you need to will also help.
Did you make any changes when you got your diagnosis as that may have been sufficient.
In any case have a look at this link as it has very good information as well as some menu plans.
https://lowcarbfreshwell.com/
Many find they will need to reduce the carbohydrates in their diet and that is quite easy by cutting out cakes, biscuits and sugary drinks including fruit juice and reducing portions of other high carb foods like potatoes, rice, pasta, bread, breakfast cereals, pastry and tropical fruits. There is still plenty you can eat basing meals on meat, fish, eggs, cheese, dairy, nuts with lots of veg and salads and fruit like berries3