Liquid argon (LAr) sampling calorimeters are employed by ATLAS experiment at the Large Hadron Collider (LHC) for all electromagnetic calorimetry in the pseudo-rapidity region |η| < 3.2, and for hadronic and forward calorimetry in the region from |η| = 1.5 to |η| = 4.9. After detector consolidation during a long shutdown, the LHC Run-2 started in 2015 and about 150 fb-1 of data at a center-of-mass energy of 13 TeV was recorded. With the end of Run-2 in 2019, a long period of shutdown began for the Phase-I detector upgrades. As part of the Phase-I upgrade, new trigger readout electronics of the ATLAS LAr calorimeter have been developed. Installation began at the start of the LHC shutdown in 2019 and is now completed, while a commissioning campaign is still underway to fully validate and improve stability of the new, higher granularity and precision Level-1 trigger system. This contribution gives an overview of the new trigger readout installation and commissioning, as well as the preparations for Run-3 detector operation and changes in the monitoring and data quality procedures to cope with the increased luminosity and pile-up.