Short answer In Pratikraman, when we stand in kayotsarga/khamāsaman for a long time, some teachers allow gently lifting one leg (or just a heel) for a moment. This is not a scriptural “rule” about left or right. It is a practical allowance to:

• maintain steadiness and alertness (avoid numbness or drowsiness),
• prevent strain so the mind can stay in equanimity,
• adjust without walking or making movements that disturb pratikraman-bhāva.

Details and tradition notes

• Which leg first? There is no fixed injunction. Either side is fine. Keep it minimal, silent, and without shifting your place or gaze.
• Shwetāmbara (Mūrtipūjaka, Sthānakvāsī, Terāpanth): Standing posture is khamāsaman. If needed, you may briefly ease pressure by lifting a heel/foot and return to stillness. No left/right rule.
• Digambara: Standing kayotsarga is with feet slightly apart and body straight. Lifting is not part of the ideal posture, but a brief, quiet adjustment is generally permitted if required to continue the austerity with focus.
• Essence to remember: The aim is inner repentance, forgiveness, and equanimity. External adjustment is only to support that aim, never to relax into casual movement.

For a simple overview of Pratikraman and its purpose, see this basic guide from JainKnowledge: and timings here: