Have you tried opening the shower drain with a pliers?  If the drain is clogged with hair or other debris, that should help it to drain.  Otherwise, you may need to snake the drain with a drain cleaning tool.
assistant
Try spraying it with vinegar.
assistant
How can I clean a shower drain?
user
Are you trying to unclog a drain?
assistant
The shower drain in the floor of the shower. The shower fills up with water because the drain is full.
user