Redshift usage in Trisquel 9

Although I now used GNOME Shell's similar feature, I still have that in ~/.config/redshift.conf from the time I was using Redshift on Trisquel 8:
[redshift]
; Set the day and night screen temperatures
temp-day=5800
temp-night=4800
; Enable/Disable a smooth transition between day and night
; 0 will cause a direct change from day to night screen temperature.
; 1 will gradually increase or decrease the screen temperature
transition=1
; Set the screen brightness. Default is 1.0
;brightness=1.0
; It is also possible to use different settings for day and night since version 1.8.
;brightness-day=0.7
;brightness-night=0.4
; Set the screen gamma (for all colors, or each color channel individually)
gamma=0.9
;gamma=0.8:0.7:0.8
; Set the location-provider: 'geoclue', 'gnome-clock', 'manual'
; type 'redshift -l list' to see possible values
; The location provider settings are in a different section.
location-provider=manual
; Set the adjustment-method: 'randr', 'vidmode'
; type 'redshift -m list' to see all possible values
; 'randr' is the preferred method, 'vidmode' is an older API
; but works in some cases when 'randr' does not.
; The adjustment method settings are in a different section.
adjustment-method=randr
; Configuration of the location-provider:
; type 'redshift -l PROVIDER:help' to see the settings
; e.g. 'redshift -l manual:help'
[manual]
lat=12.34567890
lon=12.34567890
; Configuration of the adjustment-method
; type 'redshift -m METHOD:help' to see the settings
; ex: 'redshift -m randr:help'
; In this example, randr is configured to adjust screen 1.
; Note that the numbering starts from 0, so this is actually the second screen.
[randr]
screen=0

If you do not have that file, create it, define "lat" and "lon" according to your geographic location and maybe change other settings, such as the screen temperatures. Also, you probably want to add the command redshift to the "Startup Applications".

Thank you very much Magic Banana!

your answers are always very educational.