How do I hook up an Actron 111 dwell/tachometer to my 97 Altima to check the idle speed?

Are you trying to use one of these old analog style units?
Here's some random search results - https://www.google.com/search?q=Actron+ ... ypwFePqYvM:

I'm not sure those old things will work on a 96-2000. This is the old school way to hook them up. Not sure it'll work though. https://itstillruns.com/hook-up-tach-dw ... 83180.html

Your alternatives would be using a newer digital multi meter, Actron makes one, or trusting your tach in the gauge cluster. Another option is a OBD port code tool that will give you real time info from the computer and compare that with your physical tach in the gauge cluster to see if there's any discrepancy. Then adjust idle from there.

Hope this is helpful.

Also check out the FSM graciously hosted here on-site.
It doesn't show how to hook up an external tach, but it does give the full procedure.
In this section, look for idle adjust/etc.
http://www.nicoclub.com/FSM/Altima/1997/ec.pdf

Section/page EC/7 page 159 and the lower right hand corner to find ignition coil. Dwellmeter one lead is a ground anywhere under hood and the other taps in right after the condenser and before the coil ground joins with injectors, the coil ground is wire #36 to the ECM. A typical dwell meter joins into coil primary ground after the condenser. Do NOT use the coil output to the plugs, a dwellmeter uses the primary volts not secondary which are 100X stronger and can damage the meter. The wire to resistor is the coil power (12 volt) lead in. Condenser side is primary ground out.

Make sure dwellmeter is switched to 4 cylinder.