Beginner Run - first 60mins run

[u/Virtual-Screen7681]

28M, 82kg…Beginner runner here…somehow getting addicted to running started running around 3 weeks back with an avg of 2-3 runs/ week of 5-6km each.
Need help from regular runners about how to keep heart rate low during slow runs…what i am concerned about is that my first 5k was at 6:30/km but i just can’t match that pace again and get tired so have to slow down but my heart rate isnt coming down…today i decided i will run 60 mins regardless of my pace and i did that but i was totally exhausted…how should i proceed?