Start with telling him you gotta start getting it together life’s not long and put him on a playlist , and start walking for 7 days for 25 minutes then build up from day 1 then after that week start with sit ups and walking again if okay with jogging that do that , my personal fat burn is fast exercising where you have a rope a power clean bar and weights and you use the rope to swing it and down as fast as you can till you can’t , and power cleaning with light weights than build up