Any time you work on your brakes and open the hydraulic system you will get air in the hydraulic components, air which will make your brakes feel spongy at best and may totally prevent your brakes from working. Any time there is air in the system the air needs to be removed after the system has been closed. The process is called brake bleeding. Normally air can be removed by one of a few methods. If you have a helper you can have the helper pump the brakes (always fill the master cylinder first) and hold the pressure while you open each wheel cylinder or caliper's bleeding screw sequentially and then close it and repeat the process until no more air is in the line to each wheel. Or you can use a vacuum brake bleeder and single-handedly bleed each wheel in sequence.
If, however the system has lost all its fluid it will be impossible to get the air our of the ABS control module unless you preform some complicated maneuvers with your vehicle which could be dangerous or you purchase a tool that cycles the ABS system automatically as you bleed each wheel. They may seem a bit pricey,however, if you don't have the tool you will have to take your vehicle to a shop and have them bleed the brakes, a possibly dangerous process if you have no brakes, and pay them the going hourly rate (now in 2022 $125/hr.) You could always pay a towing service to tow your vehicle to the shop fo another hundred bucks.
The tool I purchased is the INNOVA 3160RS Professional OBD2 Scanner, ABS Bleeder Scan Tool, All System Scanner
It is a multi-function scan tool which has the feature mentioned for bleeding ABS systems automatically (you still have to pump the brakes and open the bleeder screws). I chose to purchase a rather inexpensive pressure bleeder that attaches to the top of the master cylinder and eliminates the need to pump the brakes manually.
I'm sure there are others that you could use but after investigating them and buying one which falsely led me to believe it had the needed function I chose this one.
