How do I unshare a password to all collections?
You don’t. The organization you belong to effectively has its own vault. You will need to create a new entry in your own personal vault and delete the entry from the organization.
I read a discussion about this on reddit where someone pointed out that sharing a password effectively compromises it, so if you want to make it private again you should change it. Therefore, you need to create a new entry in your private vault rather than being able to unshare it.
…I’m not sure I agree with this, nor do I know if Bitwarden is working to implement an option to Unshare. But at present you will have to recreate the entry in your own vault and then delete the shared one.