First thing I'd suggest is leaving the HRM at home. It's not really useful at this point.

Second, ride lots. Every day if possible.

Third, try to keep pedaling. A steady cadence, maintained through the ride, is better than coasting. Downhill, where you can't pedal any faster than you're coasting, is allowed. And lots of fun!

Fourth, after you've been riding for a while, try to extend your trips.

Fifth, find an interesting destination. Bookstore, coffee shop, even ice cream store; ride 6 km there, tarry a while, then ride home.

Finally, keep it fun. Even if riding a bike was triggered by a "ride or die" order from a doctor, most people (very likely including you!) wouldn't keep it up if they didn't enjoy it. Vary your route, destination, speed, time of day. Power through one day, and stop and pick some daisies the next.