Beetle's lost legs. Help!

Welcome to the forum and feel at home. Make sure that the terrarium is padded with soft material like dry sand so that the beetle would not be injured in case of a fall since it has lost its supportive functions. Make sure the water provided is not deep enough in the container because it may drown and it doesn't have wriggling capabilities as well as spending some time checking it for any discomfort that may be occasioned by the tenuous state obtaining from its handicap.