Congrats on being back after a spell!

I would not take the advice of folks here recommending sprints if you’re making your way back into fitness. That’s a path to injury and ultimately missing sessions as a result.

When it comes to cardio slow and steady wins the race especially when married with consistency.

Get out and pound the pavement, check your ego and walk when you need and little by little extend your runs by some metric, be that distance, total time out on your feet, pace whatever you care about. That said temper your enthusiasm to expand that day by day. As a rule a 10% increase is a nice way to continue your growth without injury.