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In ANSYS Mechanical, in a Static Structural analysis, there is a Support called Remote Displacement. Select the face at the base of one leg and click Remote Displacement. There are 6 DOF where you can enter 0 to fix 3 translations and 3 rotations. The point will automatically have been placed at the center of the selected face, so in the Details window, type in new X, Y, Z coordinates for location of the Remote Point. Finally, there is a line item called Behavior. By default is it Deformable, change that to Rigid. Repeat on the other leg.
You said you only want to constrain translations in X, Y and Z at the clamp points. For a 3D model, that is not enough constraints to prevent rigid body motion. The structure will be able to spin around the two points. If you have 3 or more non-collinear points, you can prevent the spinning. Or you can apply a zero rotation at one or both of the two clamp points.
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