When you add an Intro Lyne step to a sequence, there is a dropdown that denotes what user you would like assigned the task to review and approve the Intro Lynes.
There is no way to create the Intro Lyne tasks without that specification, as the Intro Lynes do need to be reviewed and approved by a human before they can be saved as a property and referred to in an email template.
Once you select a User to assign the tasks to, and you launch the sequence and prospects begin to enter, whoever you choose in that dropdown will be assigned the tasks for each prospect inside of their Uptics Inbox.