if it is multiple fluid filled vesicles on the shaft then it can be herpetic lesion ,to treat it you should maintain local hygiene , use herperax or cyclovir cream or Neosporin
ointment 2-4 times daily , if these becomes painful the you can take some analgesic
, you can also take tab acyclovir
200mg 5 times a day for 5 days.
but if your lesion is single and painless the it may something else as fungal for which you should get it examined by a dermatologist
and get it managed.
thanks for consulting HCM