You can customize demographics on the Gender, Age and Geo screen when building your 3rd Party audience from either the campaign builder while creating a Performance TV Prospecting campaign, or while creating a new 3rd Party audience from the Audience Dash.
The Upload Geo Data button allows you to upload bulk geo files to your targeting or exclusion tactic. This upload option requires that the CSV file (up to 1GB in size) uploaded is formatted in a single column with only one location type (state OR dma OR zip, etc) per file upload.