Hi,
Baserow uses the ISO date format which is YYYY-MM-DD. You can use the JavaScript function toISOString() to get the date in the correct format.
If you only need the date without time or other information you can also use
{ $node["Name of the node"].json["start_date"].slice(0,10)}}
This takes the first 10 characters from a date which results in YYYY-MM-DD