Plz Help About Use Triggers To Update Other Table

Plz help

I try to use trigger to see if Component table update at same time update the AssemblySubcomponent
AssemblyID

but it say

Msg 4104, Level 16, State 1, Procedure trigupdateSubcomponentID, Line 6
The multi-part identifier "a.SubcomponentID" could not be bound.



the code look like

create trigger trigupdateAssemblyID on Component
for update, insert
as
begin
if update (ComponentID)
update AssemblySubcomponent set a.AssemblyID= i.ComponentD
from inserted i
join AssemblySubcomponent a on a.AssemblyID =i.ComponentID

end