I cant seem to get my galaxy tab screen to rotate automatically

https://www.samsung.com/us/business/support/owners/product/galaxy-tab-s-10-5-wi-fi/

https://www.samsung.com/us/support/owners/product/galaxy-tab-a-10-1-wi-fi

try resetting the tab and if problem still occurs. return it.

Allwinner A20 is a name of a processor, so I'm not sure what tablet are you using.
There is an option to block rotation, for example if you want to read an e-book while laying on your back. Go to settings and try to find an option to unlock rotation.
Also, some tablets have a hardware (physical) switch on the side that locks rotation.

Some tablets will have a physical rotate lock switch. There is also a setting that locks the rotation. Settings > Display. Auto Screen Rotate.

Try holding power button till it shuts down it may take up to 20 sec

Remove the battery and memory card, wait 60 seconds for the processor to reset, and power up.

reprogram the system

You will have to do a factory reset, which will restore the default settings on your device.

1) With the device powered off, press and hold the Volume Up and Power buttons at the same time.
2) When you see the Samsung logo, release the Power button, but continue to hold Volume Up until the recovery screen appears.
3) Use the Volume buttons to navigate the menu and select wipe data / factory reset. Press Home to choose the selection.
4) Press Volume Up to continue.

Hope this helps:

How to Hard Reset Samsung GT-P1000 Galaxy TAB:
If your Samsung GT-P1000 Galaxy TAB is frozen and unresponsive, press and hold [POWER ] for 8-10 seconds. The device will reboot automatically.
If this does not solve the problem, perform a factory data reset. In Menu
mode, select Settings ? Privacy ? Factory data reset ? Reset phone ? Erase everything.




Hard Reset Samsung GT-P1000 Galaxy TAB with keys With the Samsung Galaxy TAB turned off, press and hold the VOLUME DOWN button, and then briefly press the POWER button.

slide the drop down menu from the top of the screen (where the time and battery icons are) and click the 'Auto rotation'. that should do the trick. Cheers.