Hi @alexia_shen,
Welcome to the Bunnings Workshop community, it is wonderful to have you with us.
Is it possible to get some closer photos of the top of the window and the side you are hoping to install a new trim? I can't really see exactly what the trim was screwed into previously.
Considering the trim was screwed in previously, I would just look at replicating what was already done. It looks like there are already holes in the metal at the top.
If you shine a light in those holes, can you see if there is a coloured plastic plug in the hole? Roughly what is the diameter of the hole?
It seems likely that you'd need to use a wall plug to screw the trim back in place, which would require a hole being put in the brick with a hammer drill. If you can avoid drilling new holes in the brick, that would be ideal, so let's have a look at what was done previously and see if we can use the existing holes first. I'll wait and see what you find before assisting further.
For the new trim, yes, you could screw a piece of aluminium angle to the window frame as long as it does not block the movement of the window. You would just need to use some low-profile sheet metal screws, like these 8G x 18mm Sheet Metal Screws.
Just a reminder to be careful when doing any work around glass, as there is always some potential for the glass to shatter. Make sure you wear gloves, long protective clothing, enclosed shoes and eye protection.
Let me know if you have any further questions.
Jacob
