Book your IELTS date with British Council or IDP. To book your IELTS date you have to visit the website of IDP or British Council and go to the link for register for IELTS. There you have to fill the details about yourself and you will get a link in your mail id. Remember to collect your registration no. This is very important. Your registration no. should not be lost any how. If you do not get a registration no. for IELTS Exam, then there is no surety that you will get the IELTS date. With a registration no. for IELTS exam, you can be secure and hope t attend the test without any issue.
Once you have this registration no. , you can cross check and even modify your details by contacting the IELTS help line no. with whichever body IDP or British, you have booked your date with. Their toll free numbers are available online. You will always have to tell your passport no. at the call center of British or IDP. It is with the help of this they recognize your exam seat.
You can always change your address, email id, phone no and even the exam date (conditions apply) by using your candidate registration no., so it is not a good idea to share it with anybody.
note: Gill Sir is an official partner of both IDP and British Council. The details given here are provided with through experience of working with IDP and British Council. None of them are responsible in any way.