Beginner defeated by easy climb at the start of the trail

About a year ago I was diagnosed with with congestive heart failure and Afib. Lost about 150 lbs since then by walking and not eating vast quantites amounts of complete garbage. My weight loss has plateaued leveled out. Decided to take up MTB as a higher intensity low impact workout to get my heart rate up.

Made my way out to a beginner trail and tried for my first ride on an acutal trail that was not a paved greenbelt or a dirt path around a manmade lake. My problem is that i gas out super fast on even the most gentle inclines. How do i get better at climbing? I do not know of anywhere that easier grades that i can work up to the super beginner trail. I do want to do some tails but deffinatly feeling discouraged for that stupid easy grade.

Punching out of the ride this morning that early was worse that the slow tip over 10 feet away from my car at the trailhead.