call interface in Angular

I have an interface from the BE like this:

export interface DailyGoal extends Base {
  date: Date;
  percentage: number;
}

Now I’m trying to refer to that in my component.ts file

import { DailyGoal } from '../../interfaces';
  dailyGoal: DailyGoal[] = [];

But I don’t understand how to push the variable that I have into the date and percentage.
I created this function that will give me the list of days that the user may choose
(I still need to figure it out how to do the percentage)

   getDays(startDate: Date, endDate: Date) {
        const dates = [];
        const percentage = [];
        const currentDate = startDate;
        while (currentDate < endDate) {
          dates.push(new Date(currentDate));
          currentDate.setDate(currentDate.getDate() + 1);
        }

// for (let date of dates) {

    // if (date.getDay() <= 5) {
    //   percentage.push(100);
    // 
    // } else date.getDay() > 5;
    // percentage.push(0);


 if (startDate && endDate)  dates.push(endDate);
    return dates;
  }

how can I push my “date” variable into the interface?
hope you can help me, thank you so much