If you have embedded a Donation in another website, you may include URL parameters in the link to the parent page to prepopulate values on the embedded Donation page. To do so, include the URL parameters in the URL for the parent page itself like this:
https://www.yourparenturl.com/donate?amt=25&name=Mickey%20Mouse&company=Disney
For details on the URL parameters available to you, check out Prepopulating the donation amount and other values through a URL parameter.