Complex sentence: The agent would then return to the changed present day, compare the changed history to the uncorrupted backup record, then use Pegasus to visit the moment of alteration and restore history to its proper course.
Split into simpler sentences: The agent would then return to the changed present day, and compare the changed history to the uncorrupted, backup record of history. Then the agent would use Pegasus to visit the moment of alteration and restore history to its proper course.