As others have said you can just dump a load of soil on the top and brush it in. As long as the blades are poking through a bit it will raise itself. Maybe do it twice, 1.5cm at a time a few months apart.
Alternatively if it's a small area, you could get a kitchen knife, cut it into 1ft squares, lift them all out, put the soil underneath and relay it.
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Alternatively if it's a small area, you could get a kitchen knife, cut it into 1ft squares, lift them all out, put the soil underneath and relay it.