The current Link-OS SDK for iOS (Objective-C) only supports Bluetooth Classic (SPP). It doesn't support BLE. To use Link-OS SDK for iOS library (Objective-C) in Swift, you only need to create a Bridging Header. Please refer to "iOS / Swift, the SDK, and ZPL" on how to create a bridging header for Link-OS SDK for iOS.
If you want to use BLE, you can refer to this sample code - ZebraPrinterBLEDemo on GitHub. Though this sample code is written in Objective-C, it should provide Swift developers the enssential elements for connecting to Zebra printers over BLE. Hope this helps.