Unless you want to drop $60-100 on a tool, you need a small beam wrench.
I use this on my telescopes:
https://www.amazon.com/gp/product/B01FMXEWQC
It was cheap and readily available. 18 inch-pounds should be in the safe zone (where the wrench is accurate enough).
Otherwise, look at bicycle tools, they have a few 1-5 newton/meter click type wrenches, but the price is too high for a one time use item.
Or, just wing it by hand like every other person with a plastic valve cover does
