It's not possible to directly force yourself to go to sleep or force your body to fall asleep, although you can create practices and conditions which encourage sleep.
However you could in a way force the body to sleep by taking sleeping pills or sleeping medication which makes you drowsy and so you can more easily drift off to sleep.
Sleep is a natural process and trying to force sleep can also be counterproductive.
Instead of trying to force your body to sleep, you can try relaxation techniques, drinking some warm milk before bed and establishing a consistent sleep schedule to help the body naturally transition to sleep.
Sleep is involuntary and also a physiological process which the body regulates and not something you can control with any willpower.
The body will eventually force you to sleep if you are sleep deprived.
Even if you try to stay awake, the brain will eventually enter what is called microsleeps which are brief periods of sleep that last only seconds to compensate for the lack of sleep.
Eventually these microsleeps will become more frequent and prolonged until you fall into a deeper sleep.
As you remain awake, the pressure called sleep pressure builds up and the pressure is a result of the accumulation of a substance called adenosine in the brain.
When your sleep pressure becomes too high, the brain will involuntarily slip into microsleeps, even if you're trying to stay awake.
As sleep deprivation continues, then your cognitive and physical functions will decline and make it increasingly difficult to stay awake.
Eventually, the need to sleep becomes so strong that the brain will essentially force you to sleep, even if you resist the sleep.