Optimise Battery Use

Hi Community,
I am a rank beginner looking for advice on setting my solarPV/Battery/inverter system for optimal use of batteries on a Tiny Home. Please excuse the lack of technical insight.
The tiny house system has 2 x 3600W Pylontech batteries, 4KW of solar panels, Multiplus II 48V/5000/70, MPPT RS 450 I 100 solar controller, Cerbo GX, blue smart controller and GX display unit. Tiny home has 240V main AC supply as well. At present, system takes preferential supply from mains, rather than from batteries (Mains recharging batteries as well). How do I set up to have the tiny home to draw on batteries first, only switching to mains when battery reaches say 20% of charge?
Can anyone assist with advice on settings or programming I can make?
Thanks

Hi you will have to program the ess assistant in your system with ve configure software

See the ess manual: