Hi @stuartheth,
It looks like you have a few bricks to work with there, so you should be able to pick yourself up a bag of mortar and bed the bricks back into position. You'll need to start with the bottom course and work your way up. Since you are filling a hole, it's a little more complicated than laying a brick wall, but you should find this step-by-step guide useful: How to build a brick wall.
Have a look at the guide and please let me know if you have any questions I can assist with.
Mitchell
