5) Use a Display Text element: Insert image into the screen flow with the words "Go to NPSP Contact Merge and Search for this Record" and use the link feature with this in the link: {!LinktoContactMergeTab}
6) Save and Activate Screen Flow
Part 2: Create a Checkbox field on Contact Object
1) Create a Checkbox field called: "Possible Duplicate" on the Contact Object
Part 3: Install Unofficial SF Action that can call duplicate rules.
This will call the active duplicate rule through Apex Action.