Just like teaching kids, use a lot of hands on, a lot of drawings, and a lot of repetition, just because you said it 1000 times already doesn't mean they heard it once.
Show them a task as you do it slowly with them watching and describe each subtle movement and touch than you never think about. Then they do the task with you guiding when they get stuck.
Then they do it again, same way, and after they no longer get stuck, then they do it again later that day, and the following day, and then the following evening. and the day after.
The reason for so much repetition with breaks, is that's how the brain creates memories, you retrace the engram path to the cortex by doing it 3 times a day, morning noon and night before bed, sleep will allow the brain to form new synapses and exercise during the day will allow increased formation as well, so teach a thing, and have them go for a jog, play a game of boccie, ride a bike, have a swim or a walk etc. Then do more teaching (or have them repeat the process you taught with the notes they took) and repeat the break with more exerciser or other activities, then they need to go over it again at bed time.
Staring at a thing for hours or reciting a poem a hundred times doesn't build the engrams like 15 minutes or so of learning, followed by resting the brain and repeating 3 times a day for a week.
Some information on the function of memory and learning.