What’s the best way to reach someone in Iran given the internet restrictions?

Have you considered using Matrix.org or Element.io? These are end-to-end encrypted chat applications that might work if you can access any unofficial servers that aren't on the government's block list. However, you'd need a way to inform your relative about it, which could be tricky given the circumstances.

Your best bet might be to try contacting them via regular phone. The internet in Iran has been severely restricted, which makes internet-based communication tough right now.

Unfortunately, with the Iranian government shutting down most internet access and telecommunication services, reaching out to anyone there can become incredibly challenging. They might be blocking communications for a few reasons, including preventing protests.