FORECAST.ETS function vs Forecast Worksheet - How do i write function to add interpolated

Good evening. I am really struggling with this one. The FORECAST.ETS function and Forecast Worksheet tool are both new to me.

I have a set of data (attached)

The Data! sheet contains the raw data (dates and values)

Using the FORECAST.ETS function I have calculated the predicted rate on 12/31/2019

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I have also used the same data to create a Forecast Worksheet. The forecast Worksheet has created 4 additional dates and values (I think using interpolation??)

How would I write the function to include the calculation of these additional "interpolated" values?

Please see attached