In Jain tradition, “pre-Mahāvīra” refers to the era before Lord Mahāvīra, the 24th Tīrthaṅkara of the present time cycle.

What is known includes:

• 23 earlier Tīrthaṅkaras before Mahāvīra, beginning with Lord Ṛṣabhanātha and ending with Lord Pārśvanātha.
• These Tīrthaṅkaras are regarded as spiritual illuminators who revived the path of liberation.
• The Jain path itself is considered eternal; Tīrthaṅkaras do not create dharma, but reveal and restore it in each age.
• Pārśvanātha, the 23rd Tīrthaṅkara, is historically the closest pre-Mahāvīra Tīrthaṅkara and is especially important in Jain memory.
• In Jain cosmology, the lives of the Tīrthaṅkaras are described in the Āgamas, Purāṇic texts, and later Jain literature with detailed accounts of births, renunciation, austerity, and liberation.
• Before Mahāvīra, the śramaṇa tradition and the ideal of non-violence, renunciation, and self-discipline were already established in Jain understanding.

A simple way to say it is:

Before Mahāvīra, Jain Dharma was already present through the earlier Tīrthaṅkaras, especially Pārśvanātha, and Mahāvīra restored and clarified that eternal path for the present age.

If you want, I can also give:

• a list of the 23 pre-Mahāvīra Tīrthaṅkaras, or
• a short Jain timeline from Ṛṣabhanātha to Mahāvīra.