Q.How to support a sanseveiria?
It’s indoors and quite large and needs some support.

Your plant may need dividing.
It also could be other issues, such as inadequate light.
You can try staking the plant, but it would be a temporary solution.
These links will help you.
https://www.gardeningknowhow.com/houseplants/snake-plant/snake-plant-propagation.htm
https://www.gardeningknowhow.com/houseplants/snake-plant/snake-plant-care.htm
https://www.gardeningknowhow.com/houseplants/snake-plant/droopy-snake-plant-leaves.htm