Change which display is considered first

I have two monitors, one on a DisplayPort and another on the HDMI, xrandr -q shows this :

Screen 0: minimum 320 x 200, current 3360 x 1080, maximum 16384 x 16384
DisplayPort-0 connected primary 1920x1080+1440+0 (normal left inverted right x axis y axis) 521mm x 293mm
   1920x1080    143.85 + 165.00*  120.00   119.88   119.88    60.00    50.00    59.94  
   1680x1050     59.95  
   1280x1024     75.02    60.02  
   1440x900      59.89  
   1280x960      60.00  
   1280x800      59.81  
   1152x864      75.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
DisplayPort-1 disconnected (normal left inverted right x axis y axis)
DisplayPort-2 disconnected (normal left inverted right x axis y axis)
HDMI-A-0 connected 1440x900+0+0 (normal left inverted right x axis y axis) 410mm x 256mm
   1440x900      59.89*+
   1280x1024     75.02    60.02  
   1280x960      60.00  
   1280x800      59.89  
   1152x864      75.00  
   1280x720      60.00  
   1024x768      75.03    60.00  
   832x624       74.55  
   800x600       75.00    60.32  
   640x480       75.00    59.94  
   720x400       70.08  

It says that the DP is the primary display but GNOME says the HDMI one is display #1 while DP is #2.
How do I change that?

Please see xrandr --help:

--output <output>
    [...]
    --primary

For what?

Hello,

You posted in #support:Graphic-Cards but you did not mentioned anywhere what GPU model you have.
Please provide more information as described here:

I have a AMD Radeon 5500 XT and here’s what inxi -Fazy returns for graphics:

Graphics:
 Device-1: AMD Navi 14 [Radeon RX 5500/5500M / Pro 5500M] 
 vendor: Micro-Star MSI driver: amdgpu v: kernel bus ID: 09:00.0 
 chip ID: 1002:7340 
 Display: x11 server: X.Org 1.20.8 compositor: gnome-shell driver: amdgpu,ati 
 unloaded: modesetting,radeon alternate: fbdev,vesa display ID: :1 screens: 1 
 Screen-1: 0 s-res: 3360x1080 s-dpi: 96 s-size: 889x285mm (35.0x11.2") 
 s-diag: 934mm (36.8") 
 Monitor-1: DisplayPort-0 res: 1920x1080 dpi: 94 size: 521x293mm (20.5x11.5") 
 diag: 598mm (23.5") 
 Monitor-2: HDMI-A-0 res: 1440x900 hz: 60 dpi: 89 
 size: 410x256mm (16.1x10.1") diag: 483mm (19") 
 OpenGL: 
 renderer: Radeon RX 5500 XT (NAVI14 DRM 3.38.0 5.8.6-1-MANJARO LLVM 10.0.1) 
 v: 4.6 Mesa 20.1.7 direct render: Yes