If the LED indicator on your Dyson V6 flashes red when the vacuum is on or charging, it means the battery is faulty and the vacuum cannot be powered on or charged. The battery will need to be changed to address the flashing red light issue.
You can try resetting the battery by unplugging the charger from the wall, plugging it back in, connecting it to the vacuum, pulling the trigger and holding it for 20 seconds, and then letting go of the trigger.
Otherwise, here's the battery you'll need: https://www.dyson.com/support/journey/tools/967810-23