As others have already said just ride the bike more really. You have asked about coaching, I raced and did try both MTB coach for skills ( only briefly) and a fitness coach for fitness for a year. A skills coach of course means you have to meet and ride with them, these privately can cost a small fortune ( I know coaches who charge 100 per hour) . Fitness coaching is usually done remotely, you never have to meet the coach. you need at least a heart rate monitor and say membership of Strava so the coach can see what you are up to and keeping to his plan. I went the whole hog and had power meters. The cost of coaching will depend on the amount of analysis and support you want.
The useful things I got for fitness coaching was I was actually not trying hard enough in my training sessions but my aim was speed and power over 1 to 1.5 hrs. He gave me some numbers ie heart rate and power that I should be aiming for, I still use those numbers roughly. I suspect if you hired a coach the first thing would he would comment on was that urban riding is crap long distance training. It will help with your base fitness though. My
Commute was 23 miles each way some rural some urban. So was actually useful.
My coach was very knowledgeable ( black cat cycle coaching) and honest, we concluded I was a short sprint specialist and would never win in a race over 30 seconds long, the coaching helped me understand my limitations and strengths. I did increase my FTP ( power you can constantly kick out for 1 hr) but experience has shown I am not prepared to spend the time and effort needed to keep those levels so I am happy to be less than I could and not spend the money on a coach as well.
I have experiences of fitness coaches in the past with both my son and daughter, a lot tend not to be interested unless you may be the next big thing. If you are not the next big thing then you need to cross their palms with silver to make them interested.
You seem to be interested in going a bit faster than you do now not entering races, just aiming for one event. You do not mention whether you are overweight or underweight etc. Losing weight can up your speed as well. Also how old are you?, I started being coached at 55 and was already a experienced cyclist so my gains were marginal. If you are a over weight 25 yr old then your gains could be massive if a coach points out what you should be doing.
Good luck anyway. ( NB I am off on holiday this evening so if anyone comments on this I wont be replying for over a week )