The forgotten sanctum and getting in

Bcs, ik i have completed the quest in act 10 and have acess to the forgotten sanctum, however. I saw that i had an item that i could place down and use first before i started my journey for a sanctum, but i restarted the run thuss losing my acsess to the initial one that i gained through playing regularly. ( I am new in case you couldn't tell) So i am wondering, is my gameplay now completely ruined or do i just search for another book? In that case where and how?

It should still sit in the place you place it.