matte video(transition)

Hello. Today I launched after effects for the first time. I have a 10 second video with a transition that I would like to make matte (i.e. black and white) to use in premiere pro (track mate key). I've searched and watched video tutorials, but everyone tells you how to use a ready-made one, not create one from a video. How can I do this? I am very grateful for your help

https://preview.redd.it/4n93x7brib6d1.png?width=3199&format=png&auto=webp&s=e8ce89c06546f7bc22381aaa2c006a8ebe563532

https://preview.redd.it/ktnpt7brib6d1.png?width=3198&format=png&auto=webp&s=15bedde6749941601c55371d9458d7906f69b2d8

https://preview.redd.it/mth8xobrib6d1.png?width=3199&format=png&auto=webp&s=8fdec2620703fee4a03a8be8440f8944a5d11d5e

https://preview.redd.it/picoa9brib6d1.png?width=3199&format=png&auto=webp&s=f21628109d6b9253f09efd8ae05b32401607869e