How to???

Tell her you are going to counseling to deal with your sexual frustration issues. Than do it.

The counselor should be able to help you figure out what to do next.

If you look deeper that's probably not the only problem within your marriage.

If it was bad to start with I suspect you are saying, quite non-eventful from day dot. Are you a marine? Talking about wanting more sex to a woman in my opinion doesn't work. Women are emotional creates and respond more to feeling loved, attractive.

Ask yourself when was the last time you both laughed. The last time you bought her something for no reason. The last time you told her she looked beautiful, smiled at her and wanted nothing at all in return.

I think you will find this runs deeper and off course, you can ask yourself the same questions about when ..... where she is concerned, of making you feel like a man, looking good etc....