Thanks for the query.
These marks appear to be due to excessive collection of keratin,
You can use a keratolytic
like cotaryl or salicylic acid
This will help in removal of dead skin and will give you a soft skin.
Also use an scrub while bathing,
Dont use soda it may harm your skin.
Please meet a dermatologist
for exact diagnosis.
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
Wishing you a good health.