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You will not ruin it. It has booted into Downloaded mode. A mode you boot to download the software from computer. You can reboot and boot into recovery mode to reset it.
To do that, follow the steps below;
Turn off the phone by holding down the Power button for 10-20 seconds
Press and hold down Volume Up + Home + Power buttons at the same time for a few seconds. Make sure you hold down all these buttons at the same time to boot into Android recovery. If it doesn't boot into Android recovery, then turn it off again. Then hold down Volume Down + Home + Power at same time for a few seconds
Android system recovery will be loaded now
Select wipe data/factory reset. (Volume buttons to go up or down, select with Power button)
Select Yes — delete all user data.
Then select reboot system now
Please let me know if that didn't work, so we can continue troubleshooting.
You can remove the battery if it is not getting out of Downloading mode. Then boot into Android recovery and do the factory reset