Well done, you've got to the difficult part.
Next step, as part or my earlier long list of steps, is to figure out how to take the two sketches and merge them.
Look carefully at your prototype now, and find which pins on the Uno are free. Make a list of the pins. Call this the free list. My guess is pins 8, 9, 10, 11, 12, 13, A0, A1, A2, A3, A4, and A5.
Make a list of the in-use pins, and call that the used list. Looking at your sketch, the used list is 2, 3, 4, 5, 6 and 7. Pins 0 and 1 are used by the serial console.
From the DMD sketch, make a list of the pins that program needs. Looking at thesource code for the library, the need list is 6, 7, 8, 9, 10, 11 and 13.
Take the three lists; what you have used, what you have free, and what you need for the DMD, and sit back to try figuring out how to merge them. This is made a bit more difficult by the DMD connector which makes it harder to change which pins the DMD uses.
The conflicting pins are only 6 and 7. I could be wrong about that; you should verify everything above.
Option 1; use pins other than 6 and 7 for the LCD. Find two free pins. The A0 to A5 pins can be used as digital I/O, and the library should be fine with that. Change the sketch to use the two free pins instead of 6 and 7, run the sketch (it will fail to display anything, which is a good cross check), then disconnect from USB and power and change the wiring to match your sketch change, and then power up and see that it works. Iterate until it does.
Option 2; use pins other than 6 and 7 for the DMD. Same process in general, but you will have to replace the DMD connector with wiring, and change the DMD library. Unlike the LCD library, the DMD library doesn't have an API for choosing pins.
Your interim goal is to have a circuit prototype that you can load with either your modified LCD sketch, or your modified DMD sketch. At this goal, each sketch should make the corresponding display work, and the other display will not work, and will not hinder.
Once you've done that, the next big step is merging the two sketches, which is a software engineering or computer programming task.
p.s. tools people use for lists of pins include; paper, paper prints of the Uno pinout, spreadsheet, or comment lines in a sketch.