Findra collects nothing about the people who use it, and a contact form on this site would be the first thing here that did. So there is no form. Every route below goes to a mailbox or to a public repository, and you can see which before you use it.
Something does not work
Open an issue at https://github.com/blakazulu/findra/issues. It is the fastest route, and it is public, which means the next person with the same problem finds the answer instead of asking again.
If you attach a log from %LOCALAPPDATA%\Findra\logs\, read it first. Findra's logs record the names of files you opened from Findra and the name of any file the indexer was working on when it was slow or failed. They do not contain the contents of your files and they do not contain your search queries, but a filename can still be nobody else's business. Sending a log is a choice to share whatever is in it.
A security problem
Not the public issue tracker, and not an email. Use GitHub's private advisory form: https://github.com/blakazulu/findra/security/advisories/new
A vulnerability report is the exploit until there is a fix, which is why it does not go anywhere public. SECURITY.md says what helps in a report, what is in scope, and what to expect afterwards: https://github.com/blakazulu/findra/blob/main/SECURITY.md
Anything else
blakazulu@gmail.com. Questions about the licence, about packaging Findra somewhere, or about anything the documentation does not answer.
What is not here
There is no phone number and no postal address. Findra is one person and an open repository rather than a company, and publishing a switchboard that nobody answers would be the only dishonest thing on this website.
Replies come from a person, not a queue, so they can be slow. An issue on the repository is always faster than an email.