For the sake of argument, let us reject the hypothesis that Indian=Hindu.
Long ago we had discussed on the forum the question of "What is indianness"
The topic is archived here
Is it possible at all that "Indian" could be a set of traits that form overlapping circles on a Venn diagram so that every circle has a connection with every other circle at least indirectly via other circles.
What are cultural traits that are shared in India?
There is of course language, dress and diet.
There is also a narrative. It is the narrative of India that is predominantly Hindu. It is also the oldest narrative in India - perhaps in the world. The narrative is not just the Vedas/Upanishads at the apex, but the epic poems Ramayana and the Mahabharata but thousands upon thousands of stories, fables and parables that once again can separately be plotted as a Venn diagram that is contiguous throughout India.
We can plot two separate sets of Venn diagrams. One set is only the culture, dress and diet. Another is the Hindu narrative.
Both these sets of Venn diagrams occupy roughly the same geographic area. Both have the same people with one important difference. The Hindus can all be lumped into the Venn diagram that represents the Hindu narrative. They occcupy a place in both sets of venn diagrams. The "Hindu narrative" set is entirely Hindu, but the "Indian" set includes Hindus and non Hindus.
The "Indian" Venn diagram includes all Hindus plus some others. Christians and Muslims of India whose genes and family history place then well within the "Indian" Venn diagram claim a place here. Also included in this set are the "modern" narratives, some of which are considered "anti-Hindu"
There is a narrative of the dalits which is often worded in an anti-Hindu fashion. It too has a place in the "Indian" Venn diagram.
Apart from an early loss to Hindu geography, the main "loss" to Hindus is the loss of Hindu narrative.
If that can be accepted as an indicator of what has gone or is going regarding Hindus, the answer lies in a two pronged effort.
The first effort would be to counter the negative propaganda that has led to a loss of Hindu narrative
The second is to promote an propagate the Hindu narrative as part and parcel of India.