For a certain Profile, the access to a group of fields on object is available. How can we restrict FLS for a specific user to those fields having the above mentioned same profile.
Profile is the base level permissions, so whatever permissions you provide at the profile level will be provided to the user assigned to that profile. You cannot restrict the access which is given at profile level.
You can remove that FLS access for the group of fields from profile and provide those permissions using permission set. And assign that permission set to the list of users to whom you want to give access. This way, only the users with the permission set will be able to access those group of fields whereas the user to whom permission set is not assigned won't be able to access the fields.