There are several reasons why your tomatoes may not be turning red, along with effective methods to help them ripen.
Temperature Issues: Tomatoes ripen best between 68°F and 77°F (20°C to 25°C).
Temperatures above 85°F (29°C) can halt the production of lycopene, the pigment responsible for their red color. Conversely, temperatures below 50°F (10°C) can also inhibit ripening
Excess Nitrogen: While nitrogen is essential for growth, too much can lead to lush foliage at the expense of fruit development.
Reducing nitrogen fertilizer after fruit set can help redirect energy towards ripening
Overcrowding of Fruits: A plant overloaded with immature fruits may struggle to ripen them.
Removing some smaller, less developed tomatoes can allow the plant to focus its energy on ripening the remaining fruit