There are 2 ways these can be done. Firstly with a bulb syringe, which you can pick up on ebay for quite cheaply. Use a probiotic powder, I recommend RestoreME, as it is an all round broad spectrum probiotic powder with 10 different strains. Alternatively if you only have capsules you can open up the capsule and combine with water or you can insert the capsule directly into the anus and leave it there overnight.
Personally using the bulb syringes is a much easier and more comfortable process. Simply add 1 tsp of probiotic powder to 50ml of warm filtered water and insert this into the anus. Lay down until you feel comfortable enough that you are not going to 'leak' and allow the probiotic solution to be absorbed and retained. It is a good idea to do either of these practices before bed.
The aim of this practice is to re-innoculate the bowel and digestive tract of healthy beneficial bacteria and avoid depleting the natural microbiome.