If the prospect does not accept the rental quotation, you can mark it as lost.
Steps
Go to Rental order management > Rental quotations > All rental quotations.
In the list, find and select the desired rental quotation.
On the Action Pane, click Rental quotation.
On the Action Pane, click Follow up.
Click Lost quotation.
In the Reason lost or canceled field, enter or select a value.
Click OK.