Hi Soheli
Thanks for following up on this thread! The swim lanes that make up a pool can only be moved along with the other swim lanes as a grouped shape. This means that it's not possible to move a single swim lane within a pool or into/outside the pool.
The best way to modify a pool (to remove or add a swim lane) is by toggling the Lanes arrows in the advanced shape bar that will appear above your canvas upon selecting the pool. You can learn more about how to work with swim lanes in Lucidchart in our Diagram with Swim Lanes article.

I hope this helps! If the tips above don't address your issue please post below a screenshot of your issue and a detailed description of what you are trying to achieve so we can help you further!