<pnp:CustomActions>
  <pnp:WebCustomActions>
    <pnp:CustomAction Name="COB-SPFx-GlobalHeader" 
      Description="Adds a global header to the site" 
      Location="ClientSideExtension.ApplicationCustomizer" 
      Title="COB-SPFx-GlobalHeader" 
      ClientSideComponentId="[YOUR GUID HERE]"
      Sequence="0" 
      Rights="" 
      RegistrationType="None" />
  </pnp:WebCustomActions>
</pnp:CustomActions>