You will likely need to open the tablet to identify the processor (A50), motherboard serial number, touch chip, and WiFi chip to find a compatible ROM. Key Helpful Feature: Root Access & GApps
Some A50 tablets shipped with Android 8.1 Treble. You can flash a Generic System Image (GSI) from Google, but you must first unlock the bootloader and have a compatible kernel. This replaces only system partition, not full firmware. allwinner a50 firmware link