This can be fully accessed from the Contacts page under Connection. Export the list from the 'Connections' page and export from there. You can tick the 'Open Profile' box located at the right top of the page to select all the profiles that are open.
Once done selecting profiles that you wanted to add from your InMail campaign you can click the 'Create campaign' button at the top of the page. You'll be redirected to the sequence page where you'll be able to create your InMail sequence.
What are Open Profiles?
Open profiles are LinkedIn profiles that are public so anyone can send them InMail messages.
In that way, Alfred will only gather Open Profiles in preparation for your InMail campaign.
“Feature not available on the Personal plan”
*Available for Sales Navigator subscribers*