There are three ways to do so. You have to go to your reputation rank and you will find you need to complete Heist Battlegrounds in the playlist to increase your rank. The second method to do it is that you will need to go to the bottom of your screen and you will find three or four daily bounties there. You can complete these bounties to earn 25 reputations each. For the next method, you have to open up the upgrades and navigate to Heisted Seraphics Gear. You will find that you can get addition repeatation when a repeat drops. After that, go to your inventory and navigate to season of the Seraph armmor piece. You need to go to details and you will find that the perk on the armor piece granst 5% reputation. Each piece of armor with this perk will increase the bonus. 
