mam when i open the deleted file it just showing error message and it doesn't open it

If the flow is deleted you won't be able to recover that and it's preferred to create a new org and continue challenge.

Kindly follow the steps below to disconnect your current Agentforce Playground and create a new one. 

1. Go to a standard playground badge like this one:

2. Scroll to the bottom and click the 3 dots next to the playground listed

3. Click Manage Orgs

4. Click Create Playground

5. When it is made, refresh the page and you should be able to click Disconnect next to the Agentforce org (org starting with Epic.....)

Post these steps, navigate to your org, refresh the page and you should be able to create a new org.

If its a file, go to recycle bin and undelete the document