How to get the position of the border of a collision (MeshCollider)

Hi all,
Im blocked by a big problem,

I want to detect the red line collision position (without the blue one) to align the hand (and player to correct position) like in AAA game for climbing (ex: Dying Light, Assassin’s creed, etc…) but i dont know how, i tested with a collision but the player was not aligned correctly and it collide with the player so it’s not good to use it for that (and it will consume much resource for nothing)
so if you have an idea about how to do that, i will greatly accept.
the room in the image have a mesh collider without convex since i need it.
the player use a rigidbody with a capsule collider (correctly positioned to climb).
i know i need to stop the rigidbody velocity and disable gravity to allow the grab.
PS_2: this room is just for testing movement :b

Ive not searched on youtube, my bad :x
For some that want the info, a good tutorial is here: 1