Currently I am seeing only 3 columns for test cases. Can we Customize it or increase the columns?
Yes, If you select "Detail" view (top left above the test steps) you'll have additional columns. To create custom fields, you'll need to add those in the "manage apps" section of jira. Here's the documentation on both:
Test steps - https://support.smartbear.com/zephyr-squad-cloud/docs/tests/view-and-modify.html
Customizations - https://support.smartbear.com/zephyr-squad-cloud/docs/configure/test-execution-and-step-status.html
