An old school way of creating this effect is to stretch a nylon stocking across the lens.

In Photoshop, I would…

1. Duplicate the layer, and in Curves or Levels, ensure that it’s average value is mid grey.

2. Set its blende mode to Overlay or Soft Light.

3. If result too strong, pull the left curve handle up and the right handle down. This will kill the contrast and softer the effect.

Similar process to this….

https://rmit.instructure.com/courses/87565/pages/photoshop-u...