This means that you have oral herpes type 1, most likely. You can get genital hsv1, but if you don't have any genital symptoms, this is an oral infection.
Billions of people globally have hsv1 orally. This is the virus that causes cold sores, though 90% of those who have it never get any symptoms.
There is no way to reduce the IgG level - once you have herpes, you always have it. You could have had it for a really long time.
Herpes is only a concern for HIV if you have it genitally. Having one STD increases your risk of having another, but far more people have genital herpes (which you don't) than HIV. HIV is also easily prevented by using latex condoms every time you have sex if you are not in a completely monogamous relationship with someone who doesn't have HIV.