You can't directly change the url address (using the page SEO settings). You could possibly replace the {menu} mustache element in the page header for toDaysPage page with your own custom menu links but that's a bit of a pain to maintain. A couple of possible solutions come to mind:
301 Redirect
This is really intended to redirect traffic from an old site page to the equivalent or desired page on the current Weebly site. I haven't ever tried to apply this to redirecting traffic from a page on the Weebly site itself to another page on that site but it might work. Learn about how to do 301 redirects here: https://www.weebly.com/app/help/us/en/topics/how-to-301-redirect-an-old-page-to-a-new-weebly-page.
Use an iFrame
I'm not a big fan of iFrames but they can be useful in pinch and if properly styled and sized. In your ToDaysPage page, insert a Code Element and add the following code:
<iframe src="/cars.html" title="ToDays Page - Today's great promotion!"></iframe>
This will get the content of the desired page on to the ToDaysPage page. The downside is that it'll be in a small window. However, you can add some inline css (or make a class and add the css to the Weebly main css window) to effectively make the iframe fully responsive (i.e., no scroll bars). The page on which you'd add this code, however, can't contain anything but the iframe (so you'd need to create a new page header that contains no header and no footer and only the {content} mustache element (so that you can drop the Code Element on to the page in the Site Editor). Here's the fully-responsive iframe html pointing to the Cars page:
<iframe src="/cars.html" title="ToDays Page - Today's great promotion!" style="position:absolute; top:0; left:0; height:100%;width:100%;border:none;"></iframe>
