How to create webhook for gitlab when working with sabmodule?

Question

git

Good day.? I have a project A. It has submodules B and C. how to make it so that when pushing branches x to B or C in gitlab, a certain webhook works in gitlabe, which creates a branch with the same name x in already in project A, and pushed her.
This is necessary so that after the push, project A updates its submodules and launches its ci