LOESS is available from the Fit Line tab of the Properties panel when you edit a scatterplot in the chart editor.

1. Produce a scatter plot: menu.
2. Select any option you like.
3. Double-click the scatterplot to open it in the chart editor.
4. Select or possibly .
5. Check Loess: you can change default size of the smoothing window (expressed in % of the observations (neighborhood size of the slices) and you migth also change the default "kernel method", i.e the way the smooth values are computed: the options are in fact different weighting schemes. Uniform gives the same weight to all values, other options weight observations towards the edge of the window less.

Below you will find an example: with a loess curve added to a plot for each continent.