From the Pont d'Arsine (in Arsine, just after Villar-d'Arêne) follow the marked trail that goes back through the Romanche on the left bank. It winds through alpine fields to the sources de La Romanche, then join the moraine of the glacier of La Plate of les Agneaux. The refuge will then appear above you.
This hike through meadows at first then in high mountain, can be done without technical equipment when snowfields have melted. It takes about 5h to 6h