You can use the Influence Action to return up to two Influence Discs from your Sectors to your Influence Track. You can also Research the advanced robotics and quantum Grid Techs, which give you more Influence Discs. Finally, you can deliberately use more Influence Discs than you can Pay for in the Upkeep Phase, and thus be required to return some of the Influence Discs from your Sectors to your Influence Track.