The short answer: there are several methods for coping
The Basic Technique (“BT”) calls for masturbating your G-spot. Sometimes, stimulating the G-spot can lead to pleasure that is too intense, overwhelmingly intense. The intensity can lead to stopping masturbating.
Encountering intensity that overwhelms you is natural, and normal. The good news: there are several methods for reducing the intensity to a level which is enjoyable again.
If you encounter overwhelming intensity, there are several things to try. First, try easing up on the pressure you are applying to your G-spot. A lighter touch may be all that is needed.
Second, as orgasms was over you, intensity tends to grow over time. So, you may need to adjust, using a lighter and lighter touch as you go along.
Third, try stimulating another erogenous zone instead of your G-spot. Once you begin having orgasms, brushing or pulling on your pubic hair may provide enough stimulation. If that leads to too much intensity, try touching and rubbing only your nipples.
A combination of both brushing or pulling on your pubic hair and stimulating your nipples is also worth trying.
Fourth, try taking a couple of deep breaths. Breathing deeply tends to reduce the intensity.
Experimenting in this way will typically enable you to find a way of coping with, and managing, the intensity.
Enjoy the journey!