Trendline in Line and Clustered Column Chart

Hi everyone,

maybe I'm just not familiar enough with the new layout yet but I can't find the option to turn on a trendline in the Line and Clustured Column Chart. 

If it is not possibe, is there a way to write a measure for a trendline for the light and dark blue data? (see picture below)

I have found some dax for a trendline measure but couldn't make it working.

Thanks in advance!