After catching your wife masturbating, don't overreact. It's normal for people to have sexual needs. You could try to enhance the sexual connection between you two. Plan some romantic dates, surprise her with little gifts related to her interests. And when you do talk about what you saw, focus on how you can make your sexual relationship better together, not on blaming or shaming her.
One option is to simply pretend you didn't see it. This can avoid immediate awkwardness. However, if you think it's important to address it, wait for an appropriate time. Maybe over a cup of coffee when you're both relaxed. Then start the conversation by saying something like 'I accidentally saw something the other day, and I want to talk about it without making you uncomfortable'.
If you've caught your wife masturbating, the first step is to respect her privacy even though you've already seen it. Let her know that you love and accept her completely. You can then suggest exploring new sexual experiences together. Maybe try some new sexual positions or introduce some sex toys if both of you are comfortable with it. By approaching it in a positive and open - minded way, you can strengthen your relationship rather than let it be damaged by this incident.