“Tassa uttari karṇeṇam” actually is the first part of a full Jain Prakrit sūtra, usually recited in Samayik / Pratikraman:

Original sutra (Śvetāmbara tradition) तस्स उत्तरी‑करणेणं, पायच्छित्त‑करणेणं, विसोही‑करणेणं, विसल्ली‑करणेणं, पावाणं कम्माणं निग्घायणट्ठाए, ठामि काउस्सग्गं ॥१॥

Simple meaning (arth): For the sake of:

• removing (उत्तरी‑करणेणं) my faults,
• doing prāyaścitta (पायच्छित्त‑करणेणं – atonement/repentance),
• purifying (विसोही‑करणेणं) my soul,
• removing all śalya / inner thorns (विसल्ली‑करणेणं – like attachment, aversion etc.),
• destroying (निग्घायणट्ठाए) my pāpa‑karma (पावाणं कम्माणं),

I now remain in kāyotsarga (ठामि काउस्सग्गं) – that is, I stay motionless and aware, as a form of meditation and atonement.

In very easy language: “I want to clean all my sins, repent for them, purify myself, remove inner obstacles, and destroy bad karma. For that purpose, I now stand/sit in a still posture (kāyotsarga) for meditation.”

• This sutra is especially used in Śvetāmbara avashyaka / pratikraman as a vow for kāyotsarga.
• Digambar tradition also practices kāyotsarga and prāyaścitta, but the exact wording/sūtra text may differ according to their paddhati (ritual manuals).

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