Under Inbox > Automation, you'll find Rules. From here, you can create a new rule to reassign a conversation if it hasn't been replied to within a certain timeframe.

When creating a new rule, select the event "A new conversation hasn't received a reply", and define the time period for which your rule should wait before kicking in (available as part of Inbox Premium or a Scale plan).

You can also select various conditions under which this rule should fire (for example, you may only want this to fire for VIP customers).

Then, choose the action Assign to, and choose the team or individual to whom it should be reassigned. Save your rule, and you're good to go!