It is not super easy but manageable. Install ipatool and Apple Configurator from the app store, then login you macbook.
brew install ipatool cd ~/Desktop/ ipatool auth login -e you@example.com
This prompts for your password and 2FA code. Then find the numeric App Store ID – the digits after id in the App Store URL. For Cross DJ (free) it is 584824960.
ipatool list-versions -i 584824960
The list runs oldest to newest, so the last ID is the current version. Resolve the last few IDs now to version numbers.
ipatool get-version-metadata -i 584824960 --external-version-id <span class="s1">887600803</span>
For Cross DJ, the result was: 887600803 = 5.4.0. Then download the previous version
ipatool download -i 584824960 --external-version-id 868350149 --purchase -o CrossDJ_5_4_0.ipa
Then prepare the iPhone – back up any unsynced app data, delete the current app from the iPhone. Connect the iPhone via USB, unlock it, and trust the computer. Drag the IPA onto the device in the Apple Configurator window. On the iPhone, turn off Settings > App Store > A