So is the bottom-most rise (from carpet landing to first wood tread) currently less than 7-3/8" by the thickness of the carpet to be installed? [I'm not very familiar with carpet installations, so I'm not clear on how easy it is to measure from carpeted surfaces.]
If it's currently 7-3/8" like the others, then your first rise will be off by the thickness of the carpet you're installing. Which is allowed if the thickness is only 3/8", but that's the limit. The proper way to address it would to be lower the current treads by the necessary amount (e.g. if they are 2x, possibly replace them with plywood treads). And that would reduce your substrate height disparity at the top.
But if you've already accounted for all this, and still have a 1" disparity at the top, I don't have any great suggestions. There are "carpet shims" designed to make small ramps under carpet, but I think 1" would be more that typical.
Cheers, Wayne