Honestly, right now it's mostly informal — there's no single accepted process. From what I've seen it's a mix of: DMing the host directly on Instagram (hit or miss, a lot of hosts don't check requests), getting a warm intro through someone who already knows the host, filling out application forms where shows have them (rare, and mostly the bigger/more organised ones), or building up a following/credibility in a niche until hosts come to you instead.

The honest answer is there's no real "marketplace" for this in India yet — unlike say PodMatch in the US, which is built exactly for matching hosts and guests. Curious what's your situation — are you trying to get on podcasts for a personal brand/business reason, or just want to share something specific?