How to display warning message in self service procurement?

Summary: Display a Warning message when user submits PO as 'Accrue at Receipt' option is Checked by default

Content (please ensure you mask any confidential information):

Currently, the “Accrue at Receipt” option is checked by default. However, for certain Purchase Orders, this option should be unchecked, and users sometimes forget to update it.

The requirement is to display a warning message when the user submits the PO, prompting them to review and update the “Accrue at Receipt” field if necessary.

Could you please advise how this can be configured? I have checked via Sandbox and haven't been able to achieve this.