Request permission to open the file
Request access through Google
Open a link to the file.
On the "You need permission" page, click Request access.
The owner of the file will get an email asking for approval. After they approve your request, you'll get an email.
Contact the owner directly
If you need access right away, you can contact the owner of the file and ask them to give you access.
Try a different Google Account
If you have more than one Google Account, see if you have access to the file with a different account.
To switch to another account:
Open a link to the file.
On the "You need permission" page, click Switch accounts.
Sign in with a different Google Account and see if you can open the file.