Open a Shared Mailbox (Web)
Login with you own credentials to https://portal.office.com and go to,
Then top right go to your initials and select Open another mailbox
Then search for the name of the account and then click on it.
Login with you own credentials to https://portal.office.com and go to,
Then top right go to your initials and select Open another mailbox
Then search for the name of the account and then click on it.