Trendline Fitting

[cruckshank]

Hi! I've been trying to fit a trendline to some data I've collected. This is the first encounter I've had with Excel's trendlines not fitting the data in any shape/form, and I was hoping for someone to tell me how I can manually adjust/fit the trendline to fit my data. I have attached the data I am referring to (blue data points).

 

[cruckshank]

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