Your Drone Tweaks credentials consist of your order number and the first 8 characters of your email, up to the "@".
Username - getting the order number
Your order number can be found in the email you received right after ordering. The subject will be something like "Thanks for shopping with us (#11272)", where 11272 would be your order number. See the image below for an example.
Please make sure to also check your spam folder if you can't find the email.
The password consists of the first max 8 characters of your email, excluding the domain.