First off, rooting your tablet will prevent OTA(Over-the-air) updating in most situations, but it’s not impossible to get updates. There are ways to acquire new updates and manually flash them, but that will be more difficult than normal. It also should be noted that the A7 Lite is nearing EOL, so it might not even need to be updated soon. If you want to proceed, here are the initial steps.
First step is to unlock the bootloader. This will void the warranty of your device.
Assuming you are on OneUI 6:
Go to Settings>About tablet>Software information
Tap build number a whole lot, then enter your password(if applicable)
Close and re-open the settings app, then scroll down and click on Developer options. Then scroll down and toggle on “OEM Unlocking.” If you can’t find it, your tablet may be doomed to not be rooted unfortunately, as some carriers hide the option to unlock the bootloader(e.g. Verizon in the US).
That guide is according to my phone running OneUI 6, so it should be accurate to your Tab A7 lite.
If you have any issues, I can try to resolve them.