HTTP requests don’t include any timezone information (which is probably a good thing, because, y’know, fingerprinting and stuff). Your best bet is to figure out the timezone on the client’s end (via JS or by asking the user which might be the most sensible approach!), and send it along with whatever request you’re sending, for instance by putting it in a cookie.
Alternatively, fastly’s compute@edge allows you to use it’s geolocation service to figure out timezones - you can ask to join the community testing group if you’re interested in this but that’s definitely overkill.
Perhaps also consider if this is actually something you need to do.