Thank you for the query.
Such lump is most likely a callus
. It is nothing more than thick area of the skin which has appeared due to long, constant pressure in this area. It is some kind of protective reaction.
As you have noticed correctly, it is most likely caused by your shoes. So the best way to get rid of it will be changing shoes to more comfortable and apply in the area of this lump soft shoe insert.
You should also visit general surgeon
and consider surgical removal of this lump. However you need to know that any incision in this area is healing hardly.
Hope this will help.