Ionic + React How to return Promise<UserModel> after api call?

Ionic Framework Ionic React
1

I want to return API response JSON into a model class.

Sample code is as follows:

const authenticateUserAsync = async  (username: string, password: string) : Promise<UserModel> => {

const loginData = {
     "Username": username,
     "Password": password
}

const api = axios.create({
    baseURL: "https://www.something.com/api/services"
})

const resp = await api.post("/ValidateUserPost", loginData)

if(resp.data != null && resp.data.userId != null && resp.data.userId > 0){    
    
    //How to convert the JSON Response to Model Class
    return resp.data.map((user: UserModel) => {UserId: user.userId, FirstName: user.FirstName })

} 
else
    return NULL User Model
};

The model class which I want to return looks as below:

export interface UserModel {
    UserId: Number;
    CustomerId: number;
    FirstName:string;
    LastName:string;
}