Modify an API response

Hello
I'm new here and trying to figure out how to transform the value of a field in an API response before the final response.

What am I doing:
1) In the function stack I have an External API Request, which works perfectly
2) in the response of the external API I have
{
thingID: 3553367,
date: 12/31/2022
}

Note that the date is in dd / mm / yyyy format.

What I want to achieve:
The final answer should be:

{
thingID: 3553367, (no change)
date: (timestamp format)
}

How can this be achieved?

Thank you so much