I run 5K in about 45 minutes

Hey! I am a 25 year old man and was unfit for the past 2 or 3 years, barely passing 1500 steps a day

however for the past 3-4 months ive been trying to run 2 runs a week but Ive been struggling

Im around 70kg and 5"6 so I'm not like overweight but probs around 20% body fat

I ran about 3 5km runs so far which have been so hard to complete and haven't been able to do it in less than 43 mins

looking at the average numbers online is crazy to me than it's considered beginner level to run a 5k in 30 mins

How can I improve? thanks in advance