How can I power on when the keyboard has been disconnected internally?

Excuse the long, rambling story but I’m not savvy with this kind of stuff so I want to try and explain it the best I can.

The other night some water was spilled on my keyboard, rendering the it useless even though the track pad/screen/everything else was working fine. I wasn’t able to log into my computer without having a working keyboard so I went to the Apple store to see if they could help me. The tech helping me wasn’t able to log in using an external USB keyboard, so he took my computer, removed the back, disabled my keyboard internally, and then put the computer in some disc recoverey mode to see if he’d be able to recover my files using another computer in store. (After the keyboard was internally disabled, the external USB keyboard worked.) Right before he was about to try and and recover my files in the recovery mode , he randomly thought to have me log into Google Drive to see if the files I needed where there and they were.

He said that now that the USB keyboard was working, he could leave the internal keyboard disabled and that I would be able to use the computer with a USB keyboard, which i was fine with. He told me that I’d have to let the computer battery drain to get out of the Disc recoverey mode (since I no longer have a working power button) and then to plug my computer into a power source and it would come back on.

I did let the battery drain and the computer came back on and was functioning just fine with the external USB keyboard. I worked for a couple minutes before closing the laptop to go run errands and now I’m not sure how to get the computer back on without a power button? The laptop is now fully charged but I can’t run the battery down without turning it on?