Breathing techniques

Hi! I find my heart rate kicks up after about 2.5 miles, and I do deep breaths to slow it down, but is there any way for me to train my heart (?) for endurance outside of running and any techniques anyone follows during their runs?

I’ve been running for about a month, longest distance 7-8 miles. Avg pace 11-12, but I can do 10 for about 2 miles. I go to the gym and strength train as well.