I mistakenly cancelled my free trial. Please can you help me activate it back?

If it's an Apple service you can reach out to Apple Support here: Contact - Official Apple Support.

If it's for another app on the App Store you'll need to contact the support team for that app.

What free trial are you referring to? You will have to contact Apple Support to see if they will activate it again. You can use the Get Support link at the top of the page here to contact them.

Apple would have nothing to do with a third party developer's app or free trial.

Contact the developer of the app.

Unfortunately you cannot reactivate a free trial you canceled. You can try contacting Apple Support (assuming it's an Apple service) and see if they'll reactivate it. However, I don't think they will nor is it possible to reactivate it.

I told you what to do to contact Apple Support in my post. Use the Get Support link and see what they have to say. We are just users here like you an have no affect on Apple.

Sorry, your welcome.