I recommend several things to consider when approaching the treatment of longevity in the bedroom. Is it a problem for you, for your partner, or for both of you? If you didn’t previously define it as a problem, talk to your partner about her sexual expectations. See if you two can discover what can be added to enhance the sexual experience for her. However, if you are also distressed by your longevity, ask yourself when the problem began. Was this always a problem or is it a newer occurrence? If this is a recent problem, perhaps something has happened in your life that's affecting your bedroom performance. Do you struggle with anxiety or depression?
There is a fantastic book I recommend to men by Dr. Bernie Zilbergeld called "The New Male Sexuality." It's very informative and detailed and includes some great ideas. But, I’ll just highlight that he discusses at great length a man’s mindset when it comes to sex. Men are prescribed a wide range of mistaken beliefs that society tends to buy into, and then are disappointed when reality doesn’t live up to a Harlequin romance novel. No man is a foot-long steel rod that can pummel a partner all night and achieve orgasm without going soft, all while the partner is actively engaged and climaxing multiple times. Figure out what your realistic expectations for sex are, and what it might take to get there. Also, redefine "sex." There is lots of fun to be had beyond putting a penis in a vagina. Expand the idea into various means of play, foreplay, toys, kink, fantasy, etc.