To jump back into a previous conversation you had with {% data variables.product.prodname_copilot_short %}, tap {% octicon "kebab-horizontal" aria-label="kebab-horizontal" %} in the top right corner of the screen. Either tap on one of the last three recently modified conversations shown, or tap View all conversations {% octicon "comment-discussion" aria-hidden="true" aria-label="comment-discussion" %}. This takes you to a list of all your previous conversations with {% data variables.product.prodname_copilot_short %}.
To delete a conversation, tap {% octicon "kebab-horizontal" aria-label="kebab-horizontal" %} in the top right corner of the screen, and then tap Delete conversation {% octicon "trash" aria-hidden="true" aria-label="trash" %}. This removes the conversation from the list of previous conversations you've had with {% data variables.product.prodname_copilot_short %}.
To start over, with a new conversation, tap {% octicon "kebab-horizontal" aria-label="kebab-horizontal" %} in the top right corner of the screen, and then tap New conversation {% octicon "plus" aria-hidden="true" aria-label="plus" %}.
You should always start a new conversation if you want to ask a question that's unrelated to the current conversation.