Dell has a specific policy for pixel defects. A single stuck sub-pixel may not qualify for a replacement.
Dell's LCD Pixel Policy differentiates between different types of pixel defects. The policy is based on the number and type of defective pixels within a viewable area. A single bright pixel (a stuck sub-pixel) is often not covered unless several exist in close proximity.
You can review the exact policy details on Dell's support website at https://www.dell.com/pixelguidelines. This page defines what constitutes a defective pixel cluster and the thresholds for warranty service.
IF THAT DIDN'T WORK: Before contacting support, you can try a software-based pixel unsticking tool that rapidly cycles colors on the screen. Sometimes this can free a stuck pixel. Gently massaging the area around the pixel with a soft cloth (with the monitor off) is a last-resort physical method, but carries a risk of damage.
HEADS UP: When contacting Dell support about pixel issues, have your Service Tag ready (located on the label on the back of the monitor). They will reference their pixel policy to determine if a repair or replacement is authorized.