Where is the fill plug?

So, I ran something over about a month ago long story short have replaced a radiator, water pump, and thermostat replacement. when replacing radiator, I obviously lost some transmission fluid hence why I’m looking for the fill plug. I accidentally put transmission fluid in the engine first go around but since have done an oil change with filter and also flushed my engine. I’ve looked everywhere on this transmission and can’t find plug anywhere to fill. I do see what looks like a rubber plug or something on the side of it. Also, I see a bigger hole on the front of transmission that’s covered by a piece of stainless it looks like that pops right off and from that hole goes into the pan. Can I just fill it from there if I put my hose from the tranny bottle in it? Or not? Please help? Thanks in advance.