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Hi,
I am newbie in opensim. can you help me how to make sit to stand approach in a mot file

You can augment an existing mot file (found in your opensim resources directory) to be used for a sit to stand task. The documentation for mot files is here

Can you elaborate how can augment any mot file because I don't have coordinates for sit to stand task.

I don't have coordinates for sit to stand task

If you don't have any data, you could use someone else's data (and perform an inverse simulation) or you could develop a controller to accomplish the task (and perform a forward simulation).