in the database UI I can create a field with the type geopoint. After providing values, it looks something like this:
location: [1° N, 1° E]
I struggled to find out the right import/require. This is what worked for me !!
const firebaseAdmin = require('firebase-admin');
//other code ....
//assigning value to myLocation attribute
let newObject = {
otherAttribute:"otherAttributeValue",
myLocation: new firebaseAdmin.firestore.GeoPoint(latitude,longitude)
}