Soft brake pedal and I tried multiple times as I press the pedal, I heard sound like air pump?

I have changed brake pads and disc at rear passenger side. During the change piston was not push back so I press the brake few time piston came out and brake oil spill with it I clean the area and then push back piston it went back. I have put new brake pads and new disc. I did not top up my brake oil. now when I press my brakes it's soft and I tried multiple time as I press the pedal I hear sound like air pump. my question is what is it's solution ? do I need to bleed all to get air out ? or just brake fluid top up will do it ? or I need to install new brake caliper ? or can I drive it to the mechanic ? as brake system looks like so soft and foot goes all the way down ? need your suggestions ?
thanks,
Muhammad Usman