The grubscrews are for tensioning the blinds, the flyscreen and blackout respectively.
They need to be pushed in, and held in, with a flat bladed screwdriver and tightened, clockwise then let back out to engage with the locking mechanism.
If you let the screwdriver slip the spring will release all the tension and you start again !!!!!
The ideal tension is that when required, the blind retracts at a reasonable speed, but NOT fast enough to come to a jarring halt.
I need to replace my overhead Heinki screen in the front area, the silvering has broken down in areas, tried repainting it, but looks rubbish. looks easy enough, to replace, but will,have to wait for the lockdown to end.