did you run a cloth simulation ? that will do what you describe.

If no cloth sim , select frame 30 and do a cut (ctl z) then select frame 1 and paste (ctl v) on the keyframe editor. Then set the last frame to 1 and reply to the prompt about deleteing frames.

If you did a cloth sim just remember to work on frame 30 OR save the cloth prop as an obj (export) and then imoprt it as a prop.