if you are positive he is brumating and not sick, just reduce daylight hours to 10 hours with 14 hours 'night'. Decrease about half an hour per week till you are at 10 hours day/14 hours night. You don't really need to offer greens every day as he won't be eating during brumation and it's best he doens't eat while sleeping. If he wakes up and spends some basking and moving about the tank, offer him some greens them but not too much, just in case he goes back to sleep.
Cage temps can be lowered as well, letting it cool to as low as 65F night time and about 75-80F day time. (this is air temp, not basking surface temp).
Dragons can brumate 2-5 months but after a couple months you can simulate 'spring' by increasing daylight hours, half hour per week till you reach 14 hours day and 10 hours night. Increase air temperature so it's about 70-75F night time, 80-85F day time with normal basking temps (95-115F).
While he is brumating, there isn't anything else you need to do other than checking in on him every once in awhile to ensure he doesn't start to look like he lost alot of weight. They should not drop much weight during brumation, no more than 70g. My bearded dragon lost about 50g during her 4-5month brumation. The hardest part of brumation is missing seeing your dragon during the long months.
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PHLdyPayne