Hello , yesterday I registered my object for booking, I received a letter that I need to fill out a form in the security extranet , but unfortunately I can 't find this security column in the extranet , can you send a link ?

Hi Tagir, 

Please check under the Account tab in the top right corner then Security. If you need further assistance, please reach our to your local team. You can compose a message via the extranet under Inbox > Booking.com messages. If there is no "compose new message" directly there then click on See Contact Options > select a relevant topic eg. Account > select a relevant subtopic eg. Other > then click see all contact options > Message > write your message.