How to increase the radius of country polygons on the map?

Question

JavaScript

I'm using api nominatim to search the map. This api returns an array with the polygons of the features on the map.
For example, if I enter Paris in the search, I will get the result:

And I am already working with these coordinates.

Question:
How can this range be increased by 50 km, for example?
So that as a result I get a list of polygons in the same form.