Convert String to character if character not match will replace until it matches

/* search from database */
            String value = fname+"_"+mname+"_"+lname+"_"+bdate;
            DataBaseHelper dbh = new DataBaseHelper(SecondActivity.this);
            String holder = dbh.search(value);


            /*convertion of string search to array */
            char[] chars=holder.toCharArray();
            Character[] characters=new Character[chars.length];

                try{
                for(int x=0;x<chars.length;x ++){
                    characters[x]=chars[x];

                    if(characters[x].equals('A')){
                        // Do nothing
                    }else{
                        //replace function i dont know.
                    }

im stuck and i dont know what should i do next. I want to replace the character if it does not match the Name from the database. For example: from database: fname Robin User input: rodin since it did not match it will then replace the un-matched character until it matches the name Robin.