Do more short high effort intervals. Find a track to run at if you can and alternate easy/hard laps. The visual cues of a track will really help you feel confident pushing hard because it’s easy to see how much distance remains.
Also, check out your local running clubs on Strava. I know social running isn’t for everyone, but it’s a really good way to push your speed up. Every club I’ve run with has been psyched to get a new person.
As a second opinion, everyone is different. This is quite literally the last advice I would give anyone starting out. Short high effort intervals and spiking HR for someone with poor cardiovascular strength (myself 12 weeks ago) feels like absolute horrid shit and I would never want to go to the track again.
Prioritize enjoying the run. Which you can’t do when your body thinks you might be having a heart attack.
Also, check out your local running clubs on Strava. I know social running isn’t for everyone, but it’s a really good way to push your speed up. Every club I’ve run with has been psyched to get a new person.