How can I allow a collider in another collider

I’m making Minecraft and I’m trying to work on crouching how can I do this!!!

You can change the properties of the collider by getting a reference of it and chaing the center and size parameters. If they are box colliders you can use the following ones:

The other way, you can also get reference to the colliders and change the enabled value:

To get reference to the colliders you can create a public variable of BoxCollider type and drag them in the editor inspector or you can use GetComponents:

And filter the one you want to enable and the one you want to disable. I recommend you the first one as it is simpler to do.