300E sinking brake issue

[dealnest]

Hi guys,
I have a brake issue in my 300E and need your help.
I changed the rear brake pads and by mistake and knowing any better I opened the brake caliper. Now I have changed the pads and put everything back together, I have a problem with sinking pedal, I have to push the pedal 2 times to the floor in order to get hard brake.
My question, is this a problem because of the air I introduced into the system, or is because of some air leaking from the brake caliper, I don't see any leaking from the brake caliper, so I assume it is a air bleeding problem.
Could anyone please point me into the right direction?

Thank you all