I have free trial of a software that I want to cancel the subscription before it start but there is no cancel button. How should I do?

Free trials are cancelled the same way as a paid subscription. There is an Apple article that explains how to cancel subscriptions. Click on the following link: If you want to cancel a subscription from Apple - Apple Support

If the option to cancel a subscription is missing, see the following excerpt from Apple Support article If you want to cancel a subscription from Apple - Apple Support

You might need to scroll down to find the Cancel Subscription button. If there is no Cancel button or you see an expiration message in red text, the subscription is already canceled.

Also, a subscription that is already cancelled will typically have wording in fine print similar to "Expires on [date]" rather than "Renews on [date].”