You can access your call recording files by using the file manager app on your Android device.

Samsung – Samsung My Files

Huawei – Files

Xiaomi - Mi File Manager

Google Pixel - Files

Alternatives: Total Commander

These are located in: Internal Storage in the folder /zoiper/CallRecordings

Version differences.
Users with Zoiper Lite version up to 2.15.7 can access their Call Recordings, located at

{user_available_storage}/zoiper/CallRecordings

Version 2.16.5 and newer, Call Recordings are located in

{user_available_storage}/Android/data/{package_name}/files

NOTE: Keep in mind that you can make a backup of your current Call Recordings if you are on version 2.16.5 and want to keep these after Uninstall.

Due to Google Android 10 API level 29 changes - described here - https://developer.android.com/about/versions/10/privacy/changes

your Call Recordings will be removed if you Uninstall the application.