Hi, Your question is too general. I  need more information to address your specific problem. A swollen ankle could be due to many reasons like fluid retention, rheumatism, arthritis,  high blood pressure, varicose veins, an injury, sprain, oedema, pregnancy,  to excessive infiltration of fat, constipation, weather conditions, poor circulation, a job which require standing for hours, lack of exercise,  etc. 

However,  you could begin with a general aromatherapy treatment  which comprises a mixture of  5 drops each of Fennel essential oil and Cypress essential oil in a 15 ml vegetable base oil. Massage legs with this oil  in upward strokes from foot towards the thighs in the morning and evening.    Alternatively, you can try soaking your feet upto ankles in a basin of hot or cold water depending upon the climatic conditions to which 2 drops of Lavender essential oil is added.  Soak for 10 minutes.  This is good for tired and aching feet too and great for relaxing at the end of the day.  Do not add more than the specified drops. 

Sanna.  (Aromatherapist)