Soft continuum robot arms (CRAs) are potential in narrow confined spaces owing to the high dexterity and compliance, while torsional motion is also anticipated in some scenarios in addition to omnidirectional bending. Most existing designs generate torsional motion either relying on an independent flexible shaft or with only a limited rotation range. This article presented a control scheme for a fully self-rotatable CRA, enabling concurrent rotation along the deformable backbone while positioning the end effector. Shape configuration acts as a bridge between actuation inputs and tip pose, where the bending and rotation motions are decoupled in kinematics. With an optimization-based algorithm and Jacobian-based online correction approach, the position of the tip could be well controlled and could cope with external disturbances. Both simulation and experiments demonstrate the effectiveness of the proposed model. Results indicate that the control scheme is applicable for conventional continuum robot designs and could also perform in-situ rotation, and the motion accuracy reached around 6mm for the 120mm length manipulator. A biopsy sampling experiment also demonstrates its potential in medical applications.