If a slab has sunk or been damaged, it’s quite easy to lift and either relay or replace it. If you have spare slabs then great you are in business. If not, take a picture and the dimensions and if there is a broken bit, take that also to ensure you exactly match the size, pattern and colour. If it’s not a good match, it will be very noticeable!
Making sure you’re wearing safety goggles and heavy-duty gloves, chip out the pointing around the slab with a plugging chisel and club hammer. If kneeling, use a bit of cardboard to kneel on for protecting your knees if you don’t have knee pads. Be careful when re positioning that you do not kneel on the sharp bits you just extracted.
Lift the slab with a spade, using a timber off-cut to protect the slab next to it.
Insert a broom handle or a length of wood under the slab and roll it out of the way.
Break up and remove the old mortar using a bolster chisel and club hammer. If the slab has been laid on sand, use a piece of timber to level it and add more sand if you need to.
If the slab has been laid on mortar, wet the back and lay it (or a new slab) in position on a fresh bed of mortar mixed with four parts sharp sand to one part cement. Make sure it’s in line with the surrounding slabs. Then use a timber off-cut and the club hammer to press the slab into position, and fill the joints with dry mortar.