Open the Registry (Regedit.exe) > Current_User\Software\Microsoft\Windows\Current Version\Run > Right click in the Blank WHITE area and choose New > String Value.
A new Key will show up Called New value #1 > Right Click > Modify > Value Data should be… C:\Program Files\AVAST Software\Avast\Avastui.exe
Firstly I think we need to get more information before suggesting registry hacks.
I’m also not sure this is correct either as a user startup entry this normally has a switch after it for nogui so that the UI isn’t displayed when using the command.