Raise the grow lights a little bit each day as the seedlings grow taller. This ensures they continue to get adequate light exposure. Turn the seedling trays or pots frequently so that all sides of the plants get sun exposure.
The even lighting will prevent them from bending toward the light. Use a fan to gently blow air over the seedlings. The slight breeze will help strengthen the stems so they can better support themselves.
If the seedlings become leggy despite providing ample lighting and air circulation, it’s best to start over with proper spacing and light levels. Overcrowding and insufficient light are the main causes of spindly, weak seedlings that topple over.