Uh, thats not at all how it should work. I think youre being scammed.
Most game time additions are through the use of Codes that they send you. And then you log into the official EVE account management page, and click on “Redeem code” section and enter it.
If they are asking you for your account information, it is most likely a scam, or a RMT sale.
I would be careful if i were you. This sounds very dangerous. I would send CCP a support ticket immediately to find out if this is a legitimate site, and a legitimate sale. Anyone can sell anything on Amazon, and people sell Illegal RMT game time all the time.
EDIT: I just looked at the Amazon webpage, it does look legit, and aparently you can link your account. Ive never purchased from Amazon before so im not sure if this is actually legitimate, but it sure looks like that. In which case you would type in your existing account information. But im still not certain, so id still ask CCP if I were you. Lots of scams out there, gotta be careful.