You can use the setMaxStorageSize API to set the size of the local DB. The API is asynchronous, and the callback is called when you start App Center services. For this reason, setMaxStorageSize must be called before your call to AppCenter.start(...). You may only call the API once.
Check official docs: https://docs.microsoft.com/en-us/appcenter/sdk/other-apis/ios#storage-size