How to let my website open another website in a new window, and then fill out the forms and submit in that new window (no query params possible)?

Here we have following website: https://aspen.eccouncil.org/VerifyEval

A website should have a link, which opens that URL in a new window, then fills out the “Candidate Name” and “Certificate Number” fields on that page, then finally submits it, so the user sees the verification directly (without having to type those parameters manually).

Also the website under https://www.visa.co.uk/support/consumer/travel-support/exchange-rate-calculator.html should be opened that way (so that the script provides the parameters for the exchange rate calculation and also automatically lets them submit – so the user sees without interaction directly the conversion resuult).

I tried to use the window.open() function with javascript for the both mentioned websites, and then accessing the document property of the created object. But it failed (even if I put the new window to the focus), Chrome not worked at all, Firefox gave:

Error: Permission denied to access property “document”

What is the way to do that?