Hi, welcome to the forum. You are in a really good position to be able to reduce your HbA1C back into normal range as you have been alerted before it gets out of hand.
Some modifications to your diet by reducing your intake of carbohydrates will be a good thing to look at, as it is those that convert into glucose which is what the body struggles with. Things to be careful of are potatoes, rice, pasta, bread, pastry, cereals and the obvious cakes and biscuits and sugary drinks. The prediabetic range is from 42mmol/mol - 47mmol/mol so depending on where you are within that will determine how much you need to do from just reducing portion size to perhaps cutting out some things. Making some better food choices based on their carb value should still give you plenty of things you can eat.
Basing meals on meat, fish, eggs, cheese, vegetables and salads with small portions of the high carb foods avoiding low fat versions of dairy products as they tend to be higher carb than full fat.
Keeping an eye on the total carbohydrate content on food packing or looking on the internet shop websites can help you make a better choice.
Keeping a food diary of everything you eat and drink with an estimate of how much carb you are having and then you can make some changes to reduce that by maybe one third to start with, that may then be sufficient but in any case it is better to reduce the level slowly and gradually but also you need to be able to sustain that way of eating long term.
Have a look at the Learning Zone (orange tab at the top) and work through in your own time, but do come back with any questions you have.
There is no need to panic, slow and steady, one day at a time.