The below is the exact copy from the UK Gov - Home Office website. This is the ONLY source of information all Chagossians should follow when it comes to the Chagos Islanders British Citizenship provision.
The direct link to the website is here: https://www.gov.uk/government/publications/nationality-and-borders-bill-chagossian-nationality-factsheet/update-on-the-proposed-new-route-for-chagossian-to-acquire-british-nationality
Important information for Chagossians
Updated 5 September 2022
The application process for the new British nationality route for people of Chagossian descent is set to open on 23 November 2022.
You can apply to become a British citizen and a British Overseas Territories citizen (BOTC) through this route if:
you are a direct descendant of someone who was born on the islands that now form the British Indian Ocean Territory (BIOT), and
you are not already a British citizen or a BOTC
If you are an adult (over the age of 18), you will have five years from 23 November to apply. If you are child (under the age of 18), you will have until your 23rd birthday to apply.
The application process will be free. No fee will be required to make an application or arrange a citizenship ceremony.
You do not need to do anything yet
You do not need to do anything before 23 November. When you apply, you will need to provide evidence showing that you are a descendant of someone born on BIOT. You may wish to begin gathering this evidence now.
We will tell you how to apply
The UK Home Office will provide more information on how the application process will work before 23 November. We will share this information on the GOV.UK website.
You do not need to come to the UK to apply
You will be able to apply from your current country of residence. Your application will not be assessed sooner if you come to the UK.
Think about how you would support yourself in the UK
If you are successful in applying for British citizenship and wish to move to the UK, you need to think carefully about how you will support yourself.
Frequently asked questions
1. What kind of evidence do I need to provide when I apply?
You will need to provide evidence that you are a descendent of someone born on BIOT. Ideally, this evidence would consist of a series of birth records showing a clear line of descent between you and someone born on BIOT.
2. What happens if I don’t have that kind of evidence?
We will consider all available evidence of descent, but you will need to reasonably demonstrate that you are a descendant of someone born on BIOT. The BIOT administration is in the process of digitising the records it holds of births, marriages, and deaths on the islands now forming BIOT and this information will be used to support the decision making process.
3. What support will the UK government provide to help me apply?
We are developing an application process that will be accessible to all. We will provide more information on how the application process will work before 23 November. We will share this information on the GOV.UK website.
4. Do I have to apply for both British overseas territories citizenship and British citizenship?
All applicants will need to apply for British overseas territories citizenship. If you wish, you can acquire only this, but you can also choose to apply for British citizenship at the same time. The application process will be combined.
5. What will happen if my application is successful?
You will receive a letter inviting you to attend a citizenship ceremony, where you will receive your certificate of registration as a British citizen. This certificate will show how you obtained your citizenship.
6. Can I live on BIOT once I’m a British overseas territories citizen?
No. BOTC status does not give any legal right to reside on BIOT or any other British Overseas Territory. Those rights are governed by each territory’s local immigration laws. In the case of BIOT, the law states that no person of any nationality is able to reside there without the permission of the BIOT Administration.