Did it work prior to replacing the ribbon? If yes, then perhaps remove the ribbon and replace again. See page 19 of the manual here: https://site.xavier.edu/polt/typewriters/RoyalKMM.pdf

YouTube also has tutorials for how to thread these. (Also search for the No. 10, KH, KHM, HH, Empress, FP, etc. which also used the same general ribbon spools and set up if you can't find a KHM.) I can*t tell 100% from the photo, but the ribbon looks like it's spooling on clockwise on the right (and vice-versa for the left) and you want it the other way.

Is it not advancing regardless of which direction you have the ribbon going? Usually just one side is not working. You can use this fact to compare the typewriter bilaterally. Watch what's going on with the side that does work and compare it with the side the doesn't. What's wrong on the non-working side?

Often times the spindle on one or both sides is frozen up with dried up grease, oil, dirt, or dust. A small quirt of mineral spirits or lacquer thinner (or other degreaser) will free it up. (Here we use the mantra, a typewriter isn't really "broken" unless it's clean and broken.) See: https://boffosocko.com/2024/08/09/on-colloquial-advice-for-degreasing-cleaning-and-oiling-manual-typewriters/

reply to u/UltimateAiden98 at https://old.reddit.com/r/typewriters/comments/1f0nzt8/my_royal_kmm_ribbon_is_t_advancing_what_should_i/

Typewriter Video Series - Episode 234: Royal QDL Spacing by [[Joe Van Cleave]]