Where would I locate the a switch on a carrier blower unit that is under the house. I want to increase it to HIGH if possible. It is a fully electrical unit, no gas. Heat pump is on the outside of the house.

I doubt there is a switch for this purpose on this unit. Changing the blower speed will likely require changing the motor wiring.

In addition to KC's comment, you can't just go randomly changing your blower speed without checking the heat rise. If your way of thinking is that speeding up the blower will emit more heat from your registers then chances are the exact opposite will be true.

My finding have been the harder (faster) the blower the cooler the air being transferred