What decides if additional GA thrust required

[rudderrudderrat]

Hi de facto,

I'm not provided with tools to change my DA.

There are no tools - you just read the limits on the approach plate which satisfy your performance on the GA.
e.g. at ZRH Rwy 28, wouldn't you check if you can achieve 4% or not - else use 2.5% gradient limits?
http://www.blackholes.org.uk/PP/ZRH28