Under Inbox > Automation, you'll find Rules. From here, you can create a new rule to reassign a conversation if it contains certain keywords.

When creating a new rule, select the event "A customer sends any reply".

Then, in the conditions for your rule, select Message Content, and define the keywords you want this rule to target.

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