i accidently cancelled my apple tv free trial, can i reverse it

No. Once cancelled its gone.

https://www.apple.com/promo/pdf/EN_US_ATV+_Promo_TandCs.pdf

If you cancel during your free year, you and your family members will immediately lose access to Apple TV+ and the remainder of your 1-year free trial. You can’t reactivate this trial.

As per the terms, as stated above, you cannot reactivate the trial once cancelled. Also, in order to cancel one needs to go into an account, select the subscription, choose to cancel and then confirm the cancellation. So isn't something that can really occur accidentally. It also notifies you of the terms again in that confirmation. You are free to contact iTunes but it would be within their discretion as to if an exception is granted, and there is no guarantee.

Not by yourself. Click here and ask the iTunes Store staff for assistance.

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