Shot this with a Rolleiflex, not a Smena but, since both cameras are totally manual, it's something you can use as a starting point:
It was about 10:00 PM. Somewhat foggy. No light but street light.
Didn't use a meter or anything. Just used Kentucky windage.
There was a cement top bench right there at the edge of the waterfront. I put the camera down on the bench, aimed it where I thought it should go and pressed down on the top of the camera to keep some weight on it so it wouldn't move.
Opened the aperture all the way. Just put the shutter on "B". Pressed it in and counted "Twenty Mississippi."
Film was Tri-X Pan. Developed in D-76 1:1 for the normal time.
I did have to tweak the print a little to get it to print well but it came out all right.
For you, your aperture goes to ƒ-4, I think. You do have a "B" setting.
Just put the camera on a tripod or, somehow, buckle it down really well. Use a cable release.
From there, just click the shutter open and count to "Forty Mississippi."
Remember, with fireflies, you're going to get little zigzags in the air, not discrete dots.
Try different timings: 30 Missisippi. 60 missippi. Etc.
Experiment a little bit. Have some fun with it. You'll figure it out as you go.
It is kind of a hit-or-miss proposition. I was kind of lucky to get the shot you see above. I have done it before and they usually came out "okay." The luck was just hitting the sweet spot.
Other than that, all I can say is to go out and burn a roll of film and see what you get.