Each prospect profile has a duplicate checker on the profile itself. This will help ensure you don't have multiple profiles for your leads.
At the top of the page, you'll see a notification banner that will state that a potential duplicate has been found. You'll be able to click View Duplicates to view the results.
A pop-up will appear showing all the potential duplicates. If the lead is in fact a duplicate, you can click Merge This Prospect on the profile you want to combine. This will work just like merging a regular profile where you'll select which one should be the primary and the secondary profile will be soft deleted and all the activities combined.
If it is not a duplicate, you can click Ignore to keep the profile you're currently working on as is. Once you merge or ignore, you will not have the duplicate checker appear again unless another lead comes in that may be a potential duplicate.