With vacuuming. That's the proper way of doing it.
Small portable vacuum pumps are available for 5-10k rupees but AC installers do not want to spend a dime to purchase them and do proper installation. Pretty greedy in nature these people are. The outdoor unit stands they bring with them, they do not even bother to paint them. These stands start rusting within few months and are prone to fall with vibrations and weight of outdoor unit.