When programming a campaign, the default time zone is the one you first set when creating your Sendinblue account.
To change the time zone specifically for the sending of your campaigns, go to Campaigns > Settings. In Default Settings, click Configure. From here you will be able to change the time zone related to the sending of your campaigns. Select the new time zone and save.
❗️ Important
Changing your account time zone will not affect the sending of your campaigns. You must change the time zone from Campaigns for it to be taken into consideration when sending your campaigns.