non repairable damage related to the back cover of the device?

Firstly, to protect your rights, it's important to understand the warranty terms and conditions that come with your device. Check if accidental damage or damage caused during specific activities (like off-road biking) is covered by the warranty.

Apple One (1) Year Limited Warranty: Please read clause (d)

"This Warranty does not apply: (a) to consumable parts, such as batteries or protective coatings that are designed to diminish over time, unless failure has occurred due to a defect in materials or workmanship; (b) to cosmetic damage, including but not limited to scratches, dents and broken plastic on ports unless failure has occurred due to a defect in materials or workmanship; (c) to damage caused by use with a third party component or product that does not meet the Apple Product’s specifications (Apple Product specifications are available at www.apple.com under the technical specifications for each product and also available in stores); (d) to damage caused by accident, abuse, misuse, fire, earthquake or other external cause; (e) to damage caused by operating the Apple Product outside Apple’s published guidelines; (f) to damage caused by service (including upgrades and expansions) performed by anyone who is not a representative of Apple or an Apple Authorized Service Provider (“AASP”); (g) to an Apple Product that has been modified to alter functionality or capability without the written permission of Apple; (h) to damage caused by normal wear and tear or otherwise due to the normal aging of the Apple Product, (i) if any serial number has been removed or defaced from the Apple Product, or (j) if Apple receives information from relevant public authorities that the product has been stolen or if you are unable to deactivate passcode-enabled or other security measures designed to prevent unauthorized access to the Apple Product, and you cannot prove in any way that you are the authorized user of the product (e.g., by presenting proof of purchase)."