https://sv.forvo.com/word/chef/#sv scroll down to find the Swedish pronunciations. Try all of them, they're all different. Best I can tell, the ch- here is sort of a fshwplshfwh sound. Same as sj-, sk-, tj- stj and every single other Swedish consonant cluster. Probably easiest just to say 'chef' same as you would in English, except pretending you'd needed a tooth filled and buff bot bapf from buh benpifspt. Or, as I've heard Swedes say (about neighboring people living toward the south), like your mouth is full of mashed potatoes.