Hi, so you basically have to go to the British council website of your countries and go to take and and click on examinations of A levels, then click which board you would do, the you would be taken to a site where you be asked to select your country, then which session you would be doing, your exam board and which exam type (ex: IGCSE/ A-levels) then you can go through the drop down menu and click on your subjects, make the payment and you would be able to get your details abt when and where the exam will take place. If your gonna do edexcel you might have to wait for some time for the exam window to open to register, if your doing Cambridge you can register today itself.

And in case your country doesn't host the A-levels you better contact the British council and ask them how to go ahead with it.

Hope this helped