My Anemone moved into internal overflow box!!!!

I need some advice about how to move him out of internal overflow box please. I bought 2 small anemone then introduce them to DT evening, next day I show one stick outside at the bottom of overflow where the water can going through overflow box and other anemone was inside at the bottom of overflow box with some of tentacles hang out of overflow box.
How can I remove him out of internal overflow box?
And how can he move inside that box?
Can he going thru by those little small hole where the water enter to overflow box?
Right now, I just trying put one piece of rock to cover the light in that area, hopefully he will move out to looking for the light.
Any advice? Thanks.