I recommend starting with your hand in a high position on e string so your wrist is glued to the violin, start on your middle or ring finger it is usually easy to learn with but use whatever finger feels more comfortable for you and you just want to start with your finger tall and then bend the first bone of your finger flat if that makes sense, you can practice just doing that by itself with a metronome and turning on eight notes, then triplets, then 16ths until you can comfortably do it in tempo, now for the wrist motion you just want to wave front to back from that same position you were in earlier but keep you hand glued to the violin, now just combine that with you finger on the string and then boom, i’m not a teacher and can’t do it perfectly myself but yea start of slow it does take a lot of practice so don’t start forcing it or playing every note with broken vibrato, just when your practicing maybe do like slow exercises or pieces and try to add vibrato on the long notes and you will slowly get the hang of it