my phone has been showing yellow screen

Probably you have turned on Night Shift

• Open Control Center. Firmly press the Brightness control icon, then tap to turn Night Shift on or off.
• Go to Settings > Display & Brightness > Night Shift. 2 On the same screen, you can schedule a time for Night Shift to turn on automatically and adjust color temperature.

Use Night Shift on your iPhone, iPad, and iPod touch - Apple ...

Please see the pic below and check the status of your settings on your device.

Do you see something like this?

Please see the pic below and check the status of your settings on your device. This will remove purple/pink/colour tint