Screen pop settings are set within Salesforce Setup. To locate, type "Softphone Layouts" in the Quick Find. Click "New" to create a new layout, or if you already have a layout you want to use, click "Edit" to edit the existing layout.
Give your Layout a name, and set it as the default or assign as needed. If only one Layout is created, it will automatically be set to be the default layout. Under "Select Call Type," select Inbound (even if your organization does not use Inbound).
Under the "Softphone Layout" section, make sure that everything is assigned as needed for your business process. Most clients find Salesforce's default settings sufficient:
Under "Screen Pop Settings," you will set the outcome for what happens when Agents use Screen Pop on Campaigns and Inbound calls:
The first section, "Screen Pops Open Within," also apply to Campaigns, so this is worth configuring even if your organization does not use Inbound calling. If "Existing browser window" is selected, the current browser window will be refreshed and directed to the detail page of the current record. If "New browser window or tab" is selected, the current page will stay the same and a new tab will open on the detail page of the current record.
The other settings apply to Inbound calls. This allows you to set what happens when Agents receive an Inbound call from a known number, an unknown number, or a number with multiple matching records.