How to trace a trendline in this graph ?

[Ezzmazz]

Hello,

I am able to trace this graph :

With this code :

f(w) = (strlen(w) > 10 ? word(w, 1) . "\n" . word(w, 2) : w)

set title "CLUSTER_ALE_01"
set terminal png truecolor size 960, 720 background rgb "#eff1f0"
set output "/var/www/html/CLUSTER_ALE_01 .png"
set bmargin at screen 0.14
set key below  
set grid
set style data histogram
delta = 0.33
set style fill solid 1.00 border -1
set boxwidth 0.7 relative
set autoscale 
set format y "%g%%"
set datafile separator ","
plot 'test1.txt' using 2:xtic(f(stringcolumn(1))) title " CPU consumption (%) ", \
'' using 3 title " RAM consumption (%)", \
'' using ($0):($2+2):(sprintf(" %g%%",$2)) with labels notitle, \
'' using ($0+delta):($3+2):(sprintf("%g%%",$3)) with labels notitle

From this file :

July 2018,19%,69%
August 2018,20%,68%
September 2018,20%,61%
October 2018,21%,58%
November 2018,21%,59%
December 2018,21%,61%
January 2019,25%,69%
February 2019,27%,75%

Now, I would like to trace a trendline to know what will be the consumption of ram and cpu for MArch 2019, April 2019 to X date...

Can you show me how to do this ? Thank you !