Hi @Arash Sabet , there could be a couple reasons for this.
Make sure that you have the correct permissions to run the user flow. You need to be either a user administrator or a password administrator to run the user flow. If you don't have the correct permissions, you won't be able to see the "Run" button.
Make sure that you're using the correct directory that contains your Azure AD B2C tenant. You can check this by selecting the "Directories + subscriptions" icon in the portal toolbar and finding your Azure AD B2C directory in the "Directory name" list. If you're not using the correct directory, you won't be able to see the "Run" button.
If you've checked both of these things and you still can't see the "Run" button, try refreshing the page or logging out and logging back in. If that doesn't work, you can try deleting the user flow and creating a new one to see if that resolves the issue.
If this still doesn't work please let me know and I can help you further.
If this answer helps you please mark "Accept Answer" so other users can reference it.
Thank you,
James