My rear derailleur adjustment screws are in a vertical line there is no scew indicating inner and outer. Without removing it I can't see which screw is touching at each side of the cassette. Does the upper screw relate to the big cog or the little one?
If you look straight down into the space between the parallelogram sideplates, you may see that the outer plate has a “feeler” that contacts one limit screw, and the inner plate a feeler that contacts the other.
If that doesn’t work, we can’t guess without knowing what kind of derailleur you have, and you can probably find service info on the manufacturer’s website.
If you look at the rear derailleur upper jockey wheel from the back of the bike, you can see the limit screws working as they are adjusted, and see which screw effects which setting.
It's a bit awkward to arrange the bike to get a good view of the derailleur cage. Putting the bike in a work-stand with the front wheel lower than the rear is best, but you can also prop the back wheel up on something and have someone hold the bike upright, or you can put it upside down on its bars and seat (being careful to not scratch up seat, shifters or brake levers or course).
To see the inner limit screw working you'll need to shift to the highest gear and manually push the derailleur inwards (not by the cage though, you could bend it).
To see the outer limit screw working you'll need to shift to the lowest gear. Note that the cable will stop the derailleur moving outward at some point.
Keep track of the number of turns adjustment you make to each limit screw if you want to put them back where they were before starting.