Flashing firmware wipes all internal storage. Backup photos, contacts, and documents to a PC or cloud storage.
You can find the stock firmware files for the SM-T285 on several trusted platforms:
To manually flash the firmware (the "Stock ROM"), you will need a Windows PC and the following software:
Sites like SamFW and SamMobile offer the same files via slow servers for free users.
Before you begin the download or installation process, ensure you have the following: Backup Your Data