How to downgrade swift version too 3xx in Xcode?

Question

Apple Xcode

Hello! Is it possible somehow to use swift 3xx in the latest Xcode ( 10 2 beta ) ?
What is the actual problem - there is an ionic project that implements an audio chat using webrtc using the ios cordova plugin: iosrtc ( https://github.com/BasqueVoIPMafia/cordova-plugin-... )
Unfortunately, the plugin stopped working with swift version 4+ And, in turn, the audio chat stopped working on ios devices (In the plugin repository there is a topic where people are looking for people to upgrade the plugin, but such things can take months, and as always there is no time =(