You can find quite a few YouTube videos of pilots using range extenders on their Mavic Air's with varying degrees of success. But honestly, flying in urban locations is going to be wildly variable even with range extenders. One simple thing you can try is setting a manual Wifi frequency and channel. Normally, 5.8ghz is recommended in urban locations, and picking a channel manually from within the app may give you better results than auto. But don't expect anything near the advertised range in urban locations. In my area - which is an urban area with approximately 500,000 - I usually get no more than 1 mile, and even that is rare. I generally get between 1/2 mile to 1 mile (FCC) but it is wildly variable, as I mentioned. You are not only dealing with Wifi congestion and radio interference, but usually large obstacles that also affect your signal. The example where I got 1 mile was when I was on top of a pretty big hill flying where there were no obstacles between me and the aircraft, and I thought 1 mile was very good. Conversely, when I flew downtown trying to capture an arena when it was empty, I literally lost signal on the other side of the arena because the building blocked the signal.
Flying an aircraft that uses a different radio transmission type like the Mavic Pro with its Occusync or the Phantom with Lightbridge will yield better results, but even they can have problems in urban locations. It's just the nature of radio physics. Ultimately, try choosing manual settings like I suggested or do some research on range extenders (in the forums and on YouTube). Some extenders are as simple as attaching to the back of your remote to direct the signals toward your aircraft, while others require rewiring your remote. Good luck! Personally, I just accept the limitations in urban areas and fly safely within short distances. Others will recommend not flying at all in urban locations.