Get some shrub and soil for the floor of the cage and have a stick or two in there more something to cling on it. If u have a lid with air holes in and it is at the top all the time, do one of these two things:1. Get some flies so the food can reach the mantid.
2. Take off the lid with the mantid on it and drop a small insect in front of it (1/3 of it's size, if it is a cricket or locust you may want to break the back legs by crushing them with ur fingers.
You seem to be in the same situation I was in with my 1st mantid. I still only have 1 but it was very small when I got it. I got a Giant Indian Mantis which are closely related to the Giant Asian Mantis so care should be similar.
For mine I keep it at 24C and spray it with a spray bottle every 2 days and my mantid is fine.
Hope it turns out well 4 you.