Above code would not help you. You have multiple records and you play with one imagebutton all the while.
Instead of using DataReader, use DataAdapter to fetch the data. Once you have data in a datatable/dataset, then loop through each row of it and set the imagebutton url for that row accordingly.
BTW, above SQL query, how do you know which seat numbers are not booked? I guess, you have to fetch that data too OR you hardcode it as you already know how many seats are there in totdal. Once you have that then your data would be something like:
Data 1 (seats reserved based on date & time):
Date 2 (based on your design that there are 6 seats in total):
Resulting Datatable you should aim to get:
seat No | IsReserved
Now, create an outer loop of Data2 and an inner loop of Data1. Basically, you need to check what all Data2 seat numbers are in Data1. When you find a match, set isreserved flag or change the image button source as per your need.