Valve cover replacement leaking

Hello
I replaced yesterday the driver side valve cover ,every thing was ok I put the new one and closed the screws back.
This morning I start the engine and wanted to go to work and oil start to spray out from the valve cover.
I turn the engine off and went to work.
Now my question is in assumption that I didn't turn the screws at the right moment how do I get to the back screws with something that can close it at the right moment???
What tool do I need?

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