Open the terminal and enter the following command:

Step 1

xrandr

Output:

Virtual1 connected primary 1440x900+0+0 (normal left inverted right x axis y axis) 0mm x 0mm

View the currently connected display device Virtual1

2 Steps

gtf 800 480 60

output

# 800x480 @ 60.00 Hz (GTF) hsync: 29.82 kHz; pclk: 29.58 MHz
 Modeline "800x480_60.00"  29.58  800 816 896 992  480 481 484 497  -HSync +Vsync

3 Steps

xrandr --newmode  "800x480_60.00"  29.58  800 816 896 992  480 481 484 497  -HSync +Vsync

4 Steps

xrandr --addmode Virtual1 "800x480_60.00"

5 Steps

xrandr --output Virtual1 --mode "800x480_60.00" 

6 Steps

//Following is persistent display mode

//1
Edit Profile ~/.config/Monitors.xmlTo configure the resolution size, but will not take effect until the next reboot

<monitors version="1">
  <configuration>
      <clone>no</clone>
      <output name="Virtual1">
          <vendor>???</vendor>
          <product>0x0000</product>
          <serial>0x00000000</serial>
          <width>800</width>
          <height>480</height>
          <rate>60</rate>
          <x>0</x>
          <y>0</y>
          <rotation>normal</rotation>
          <reflect_x>no</reflect_x>
          <reflect_y>no</reflect_y>
          <primary>yes</primary>
      </output>
      <output name="Virtual2">
      </output>
      <output name="Virtual3">
      </output>
      <output name="Virtual4">
      </output>
      <output name="Virtual5">
      </output>
      <output name="Virtual6">
      </output>
      <output name="Virtual7">
      </output>
      <output name="Virtual8">
      </output>
  </configuration>
</monitors>

//2
Sudo gedit/etc/X11/xorg.conf//Open (or New)Xorg.confFile, the initial system does not have this file, you can create it.
After opening, add the following to the file:

Section "Monitor"
    Identifier "Configured Monitor"
    Modeline "800x480_60.00"  29.58  800 816 896 992  480 481 484 497  -HSync +Vsync    #Output from command gtf
    Option "PreferredMode" "800x480_60.00"    #The pattern name is "800x480_60.00"
EndSection


Section "Screen"
    Identifier "Default Screen"
    Monitor "Configured Monitor"
    Device "Configured Video Device"
EndSection


Section "Device"
    Identifier "Configured Video Device"
EndSection

Finish, Restart, OK