Short answer: There is no fixed “conversion” in Jain scriptures that says a certain number of Navkar Mantras equals one full Pratikraman.

Important points:

• Pratikraman is a complete rite (alocanā, pratyākhyān, kayotsarga, sutras, forgiveness, etc.). It cannot be replaced by counting Navkar Mantras.
• In the Shwetambar Samvatsari Pratikraman, a traditional prayashchitta inside the rite allows either 40 Logassa or 1008 Navkar Mantras. This is only for that part of the ritual, not for the whole Pratikraman.
• Digambar and Shwetambar both emphasize bhav (right intention) and doing the full Pratikraman at its prescribed times; extra Navkar japa is meritorious but not a substitute.

If you cannot attend or perform the full rite, recite the Navkar Mantra with pure bhav (many follow 108 or 1008 counts on special days), but treat it as additional merit, not as “one Pratikraman.”