Hello nneja938,
We understand that you're unable to make a conference call and a few of your settings are missing. We'd like to provide you with a few steps that may help resolve these issues:
• Restart your iPhone
1. Press and hold either volume button and the side button until the power-off slider appears.

2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.
• Manually update your carrier settings
1. Make sure that your device is connected to Wi-Fi or a cellular network.
2. Tap Settings > General > About.
3. Follow the onscreen instructions to install your carrier update.
• Reset your Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before. Please be sure to make a note of your settings prior to completing this step.
Go to Settings > General > Transfer or Reset [Device] > Reset > Reset Network Settings.
Let us know if this helps.
Best wishes.