According to Jain scriptures, the main and special “gift” Indra gave to Neminath Bhagwan was:

Indra gave him the name “Neminath” (Arishtanemi).

• At the time of Janma Kalyanak (birth celebration), Indra (Saudharmendra) performed the abhishek (holy bath) of the Tirthankar child and then named him “Neminath”, seeing him as the nemi (rim) of the wheel of dharma – the one who protects and supports dharma.
• Along with this, Indra and other devas also:

- Bathed him with divine water (1008 kalash), - Dressed him in divine clothes, - Adorned him with ornaments, - Performed grand pooja and celebrations.

But if your question is specifically “what did Indra give?”, the most important and remembered thing is: