To play on a private server, type the server IP and overwrite the regionInfo.dat file in Internal Storage/Android/data/com.innersloth.spacemafia/files.
There are two methods to play on a private server on iOS, both of which require a jailbreak.
You can install the ImpostorConfig tweak from pixelomer's repo on your jailbroken device. Add to Cydia
Type the server IP and overwrite the regionInfo.dat file in /var/mobile/Containers/Data/Application/Among Us/Documents using Filza.
To play on a private server follow the following steps:
regionInfo.dat and doesn't have additional numbers (e.g.
regionInfo (1).dat) because you downloaded it multiple times.