I agree with DanielWillis 's approach and would use the same. The part of the url after the Question Mark (?) is called the Query String. It is name value pairs seperated by Ampersands (&). The job you have now is to look into the html of the NS webpage and find the form element names of the dropdowns you want to set the value in.
Usually a dropdown will look like this:
<select id="account" name="account">
<option value="1">30000</option>
<option value="2">30001</option>
<option value="3">30002</option>
<option value="4">30003</option>
</select>
You want the left side of the Equals(=) to have the Name of the select, account in this case, and the right side set to the value or option value of the account you want.
Here's the rub: The web page that receives the query must have code in it to receive the URL Query string and parse it to set the values in the page controls.
If you have access to code in the page, you can add JQuery to marshall your Query string into the right contol:
$(document).ready(function() {
// Deconstruct the current browser URL
var url = new URL(document.location);
// Get query string
var params = url.searchParams;
// Get value of the account from the query string
var acctVal = params.get("account");
// Set the account as the value of the dropdown
$("#account").val(acctVal );
});
