In many Jain traditions, before starting Logassa Kausagga, the usual mantra spoken is the Navkar Mantra.

Common sequence is:

1. Navkar Mantra
2. Then Logassa Kausagga

In some traditions, Iriyavahiya may also be done before Kausagga if needed, especially after movement or before standing in kayotsarga.

Simple answer: Navkar Mantra is generally recited before Logassa Kausagga in Chaitri Poonam.

If you want, I can also give you the exact sequence of prayers for Chaitri Poonam in Jain practice.