Communication is the best way to avoid overlap when working with a UI/UX designer. The product owner should have an understanding of what their goals are, and these goals should be outlined in writing. The UI/UX designer should also have access to this information. This will allow them to know what the product owner is looking for, so they can produce designs that match those specifications.
Some specific instruments may be handy:
Wireframing and prototyping tools: Sketch, Figma, Adobe XD
Communication and collaboration tools: Trello, Slack, Asana, Jira
User testing and feedback tools: UserTesting, Hotjar