Blockchain's job is not to limit or remove access to data.  That is the job of programs that access it and to decrypt it.  It is for having independent verification of the legitimacy of the data by having addtions of information to its database timestamped, compared and set in stone.  That way no one can hack into it to change the information because copies of similar database are stored in many servers and can be verified for its authencity at anytime.