Diagnosis
A sub-pixel is stuck in the 'on' position, displaying a constant red color. This is a physical hardware anomaly, not usually a software issue.
How to Fix It
First, attempt to un-stick the pixel using gentle software methods. Run a dedicated pixel-exerciser website or YouTube video that rapidly flashes red, green, blue, and white full-screen colors for 30-60 minutes. Alternatively, apply very gentle, localized pressure. Power off the monitor. Place a soft microfiber cloth over the pixel. Use the rounded end of a pen (not the tip) to apply light pressure directly on the pixel location for 5-10 seconds. Power on and check.
If That Didn't Work
Check Dell's official pixel policy for your region. Many regions have a policy requiring a minimum number of defective pixels (e.g., 6 or more) for a warranty replacement. A single stuck pixel often does not qualify.
Heads Up
Do not use excessive pressure or sharp objects. You risk creating more dead pixels or damaging the LCD layers, which would void your warranty. The 'pressure' method has a low success rate and carries risk.