I saw in your image an axis that is available. If that axis is not in the correct location create one that is.

With the Select tool active (keyboard S) select the circular edge.

Activate the Pull tool (keyboard P).  An onscreen menu will popup. Click the Axis button then select the axis.

Drag the edge and see the bend surface revolve about the axis. Type in 90 in the popup angle field and hit enter to get a 90 degree bend surface.