Studio 26c does not have a control panel. Only the option to change sample rate and ASIO buffer size.
Universal Control will display the Studio 26c.
Only more complex devices like Studio 1810, 1824, Studio 192, StudioLive mixers, etc have mixer control panels.
Try uninstalling UC from the Programs and Features menu in Windows Control Panel.
Download Universal Control from the download page, right click and select "Run As Administrator" to install.
If you're still having issues log a support request at
https://support.presonus.com so a support tech can help you directly.