Access the secondary mailbox, open the Settings section, select Forwarding and POP / IMAP and enter the address of the main mailbox.
Go back to the main account, go to Settings , select Multiple Inboxes and enter the command to: xyz@gmail.com (secondary email address) into Pane 0 and other e-mail addresses on the next Pane if there are multiple Gmail accounts. .
At this point, the new email of the secondary email will automatically show up in the main account in the right column. Google supports opening up to 8 new subdivisions in Inbox for users to conveniently view multiple mailboxes.
The most obvious benefit of using the main Gmail account saves time. You do not need to switch your account anymore.
I wish you all success!