User Level Security

We are using PSFSCM 9.2 with zero image and PT 8.53 the security is set as per the snapshot below as we have two separate books (two legal separate entities) and our objectives to achieve by setting the security in this way are below two:

1- We want a user to access only one book at a time and not the other

OR

2- A User to access both books. ACESS BOTH BOOKS .

Kindly let us know what other by USER_ID navigations available on the navigation path Main Menu -> Setup Financials/Supply Chain -> Security --> ....... we need to use to achieve the above objective of ours.