Adding additional Regarding in email conversation

Using the Dynamics Outlook App (not Client), after the initial Regarding has been set how do you later in a conversation add extra Regarding(s), e.g. Tracking against a Lead that Lead becomes an Opportunity and then one or more Quotes and even multiple Projects (using Project Service Automation). How do you add these extra Regarding(s) during the conversation history as the only options seems to be to Untrack or add Activities?