How do I connect the virtual ground of rail splitter?

Keep it like this. Use your vrtual ground for your opamp inputs.
Realize that you will need to send negatve voltage (relative to your virtual ground) to your arduino. Anything above 0.5V will damage your arduino (as it sees 1V relatve to virtual ground as 5.5V).
You cannot sink large current to your virtual ground...
That is als why you cannot use your virtual ground as arduino ground.