Thank you it works for me too with volumio 3.198
My LCD is in landscape with hdmi port at the bottom.
What I’ve done :
Installed “Touch Display Plugin” (I tried to install 3.3.3 but it seems that 3.3.1 is finally installed 
).
(Activating temporarily “show mouse pointer” in this plugin is useful to calibrate your touch screen).
wget https://github.com/goodtft/LCD-show/raw/master/usr/tft35a-overlay.dtb
sudo cp tft35a-overlay.dtb /boot/overlays/tft35a.dtbo
nano /boot/userconfig.txt
#==== Put this in this file : ====
dtparam=spi=on
dtoverlay=tft35a:rotate=90
#===============================
wget https://raw.githubusercontent.com/goodtft/LCD-show/master/usr/99-calibration.conf-35-0
sudo cp 99-calibration.conf-35-0 /etc/X11/xorg.conf.d/99-calibration.conf
sudo wget https://raw.githubusercontent.com/goodtft/LCD-show/master/usr/99-fbturbo.conf -P /usr/share/X11/xorg.conf.d
sudo nano /usr/share/X11/xorg.conf.d/99-fbturbo.conf
#and change
Driver "fbturbo"
#to
Driver "fbdev"
# To rotate de touch input (landscape with hdmi at the bottom)
sudo nano /etc/X11/xorg.conf.d/99-swapxy.conf
#==== Put this in this file : ====
Section "InputClass"
Identifier "SwapXY"
Option "TransformationMatrix" "0 -1 1 1 0 0 0 0 1"
MatchIsTouchscreen "on"
EndSection
#===============================
Installing “Now Playing” and in settings click on “Volumio Kiosk” offers a better view for a little 3.5 inch LCD !