How to Plot Linear fit for only given intervals of x in xy plot

[JP187]

I want to a plot a linear fit as shown (in cyan) between the x axis values as choosen which should be user defined .  I tried to filter out the x axis array greater than lower limit and less than upper limit and plot but due to rest  of data in array as NaN the linear fit doesnt work.

please help!!

[VA.KI]

Hello JP187,

How did you filter given portion of array?

Why you haven't use subtract portion function?

Could you please attach the the code?