The phrase "to increase the bonus" means to make the extra reward given to someone for their work or achievements even bigger or higher. Full definition
Extra credits will make up the bulk of rewards; from daily login gifts to increasing bonuses for podium finishes and rank promotion. (gtplanet.net)
If all they wanted to do was reward premium business, they could have increased bonus miles for premium cabin fares. (viewfromthewing.boardingarea.com)
Is increasing the bonus by only 5,000 miles enough to go from worst to first? (travelcodex.com)