I have multiple sclerosis and limited mobility. How do I get a free government grant to remodel my shower?

You might not need to do that. Call your village hall, your township office, and your county human resources department. One or all of them will know of area individuals and groups that do all kinds of work for seniors and the disabled, and will know how to connect you to sources for funding any improvements to your home.

Not sure what country, I will have to answer for the US, no there is not grants, often there may be a million dollar grant to a local company that takes applicaatoins locally

But most of the many will come from local non profits. Have you contacted the local MS office