Patiently, is probably the best way! Unless you have a cell sorter. You will need to continuously carry out single cell isolations in a well plate moving the cell of interest into clean, appropriate media under species specific optimal conditions until that cell divides to become the dominant strain. At that point you may be able to carry over more than one cell into a fresh well. Then, it may be necessary to treat the new culture with antibiotic or anifungal agents. Sadly, it will not always be possible, as many species will not tolerate the conditions of single cell culture. Best of luck with it!