Hi @Kuhnshar,
Thank you for your question about repairing pool pavers and welcome to the Bunnings Workshop community, it is fantastic to have you with us.
My suggestion is to remove the loose pavers, clean them up, and reattach them using mortar.
Depending on how loose the pavers are, it may be very easy to remove them, however, if you have some trouble, a cold chisel hit with a hammer, directed at the existing mortar would help to loosen things up.
Once removed, clean the void where the paver originally was using the cold chisel and hammer to break off any of the remaining mortar.
Once the big chunks are out, use a wire brush to remove any smaller loose material, so it is taken back to a relatively clean area.
After cleaning and preparing the area, mix your mortar following the manufacturer's instructions and apply it to the bottom and sides of the mortar using a brick trowel. Keep in mind that you will want enough mortar so that it spreads when you press it into place and fills the voids around the paver. Tamping the paver with the back of the brick trowel can help vibrate the mortar and fill the voids around it.
You might like to check out How To Build a Brick Wall for some guidance on a similar process.
Let me know if you have any further questions.
Jacob
