Feels like this should be simple?

In the above example I want to lookup B5 and insert into col 4 (G) the value in A5 - that was easy enough but then I need it to populate cols up to the col in C5 with the same value (A5)

so it looks like this:

The values in B5 and C5 will change in subsequent rows.

I have been trying things for days now and am pulling out my hair, it seems like it should be simple?

Any help appreciated.

Reagrds

Nigel