Hi, many thanks for the query!
As far as the site of the lump is concerned, it could be a "ganglion", a benign swelling arising from tendon sheath, also it can be a lipoma
or less likely an implantation dermoid
Now we need to examine it for its consistency, mobility, its movement on movement of the finger etc to come to a clinical diagnosis.
Nothing to be worried for,
it can be removed under local anaesthesia by a general surgeon
& excised specimen to be sent for histopathological examination.
Wish you a good health. Take care.