Some restaurant updated their online ordering website and some don't.
Some also state what deal they have in the Restaurant Week Overview page of the restaurant under the ToGo Offer section, scroll down to see it.
For Casa Del Chef Bistro, seem like you need to call them for detail:
https://www.nycgo.com/restaurant-week/browse/4086
NYC Restaurant Week To Go Offer
Now through January 31, enjoy a special offer on takeout and delivery during lunch or dinner. For just $20.21, you'll get a prix-fixe entrée and at least one side during lunch or dinner. Contact the restaurant for more details.To get $10 off, from the Mastercard register page's term and condition.
Registered Mastercard Cardholders for NYC Restaurant Week To Go: Starting on January 25, 2021, through January 31, 2021, or while supplies last, the $20.21 amount spent on NYC Restaurant Week To Go qualifies for the All In NYC: Neighborhood Getaways statement credit; therefore when you spend $20.21 (or more) for the NYC Restaurant Week To Go meal(s) in a single transaction on your registered Mastercard® credit or debit card at participating restaurants, you will receive the All In NYC: Neighborhood Getaways statement credit ($10 statement credit for spending $20 or more on a per transaction basis) on your registered Mastercard account (within approximately 5 business days of the date of qualifying purchase). The promotion may end prior to January 31, 2021, subject to NYC & Company and Mastercard’s discretion.
NYC Restaurant Week To Go is available for participating restaurants with delivery and take out options through the individual restaurant’s website and/or through Seamless, Grubhub or Tock (please see individual restaurants for options). For a list of participating restaurants please go to nycgo.com/rw. The promotion is not available for dine-in at all participating restaurants, so please check with each restaurant beforehand. For updated information on coronavirus cases in your area, please visit the NYC Health Department’s website. Studies indicate that there is a lower exposure risk when outdoors, but the level of risk involved with patio dining is contingent on restaurants following strict social distancing and other safety guidelines.
Mastercard Statement Credit:
Exceptions may apply to each of the above programs (All In NYC: Neighborhood Getaways or NYC Restaurant Week To Go) and are at NYC & Company’s sole discretion. The credits received for All In NYC: Neighborhood Getaways on an individual Mastercard cannot exceed $100. Cardholders may receive up to $100 total in statement credits for the duration of the promotion when eligible.