Just like any other day

You literally can open it with your hands. But if you don’t have the strength or it hurts too much, pretty much any object that will fit in the hole where the shaft for the knob passes through will release the mechanism. Many household objects such as screw drivers, flatware, hair styling tools, possibly a tooth brush or even a hanger could work. You can also slide a card or similar, thin, flat, semi sturdy object between the frame and the latch plate. Two screws is all that is required to remove the latch assembly and never have the problem again, but with 2 screws you could just install a new doorknob anyway. Maybe this person doesn’t know this.... but they obviously had a phone and internet since they posted and spoke in the present tense, and the information is easily found online.

Happened to my once at uni. My friend forgot to the put the handle on and we left the room... At 2am. I was stuck outside my door but she kicked the door hard to get rid of the other handle and I used a knife to twist the thing that turns the door

What a good brother!!