5k training after heart attack - need important advise re high HR

Good morning.

I'm M45, had a heart attack 7 month ago. After last heart cartography under pressure i was told by a doctor that my max HR is around 159, so this year i shouldn't go over 140 during physical activities.

Have been doing fast walks 6 days a week for last 4 months (8-9 km every walk). Today was my "benchmark run" with garmin coach in order to start 5k training. I had to run for 5 minutes... here is the log https://connect.garmin.com/modern/activity/4299534738. As you can see i ran with tempo of 6 min/km, but my heart rate went up to 163.

So, i need an advise from people who've been in the similar situation. What do i do... should i accept the fact that i can't run at all and stick with my walks for physical activity or do i tough it out and wait for my heart to get trained enough so HR during runs would lower itself?

Thank you