Change multiple trendlines on one chart

I have one chart on the worksheet which I am going to use to cycle different data through.

I've set this case statement up to change the trendlines, but now that I've added more, how can I change them all without repeating the seriescollection over and over six times?

Also, for the Parabola chart, changing the trendline doesn't seem to be as straightforward. What I have it the code below doesn't work? Any suggestions?

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I'd call another sub and loop the series

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Thank you Joseph this works great