I'm hoping for some suggestions for a small project:

I have some photos taken during the recent annular solar eclipse, of the surrounding land, as the Sun was progressively covered.
Since they were taken with my iPhone, the images all look equally exposed, as expected, but the exposure times from the EXIF data vary broadly with the light level, from 1/1770 second to 1/96 second, f/2.8, ISO 64.

How can I "reverse adjust" the images, to approximate the effective exposure, as if they were all taken at one shutter speed, say close to the shortest, 1/1770?

I can easily enough use one or another tool to darken the images, but I'd like to do it quantitatively...