Try this: 1. Open the Phone app. 2. Click the 3 dots menu in upper right. 3. Select settings. 4. Click on Supplementary services. Here you can setup call forwarding and call waiting.
Be aware that some carriers block the Supplementary services menu on the phone.
Who is your carrier and is your device locked or unlocked? Certain carriers disable the supplementary services. I don't know for what earthly reason they would do that, but they do.
