There's no single fix for inbox placement, but a few real things make the biggest difference.
Verify your domain, and add SPF/DMARC
Verifying your sending domain is what lets your mail be signed with DKIM in the first place - without it, you can't send from your own domain at all. SPF and DMARC are optional on top of that, but both genuinely improve how Gmail, Yahoo and other inboxes trust your mail.
Until your own domain is verified, sending still works - your mail goes out through our shared platform domain with your address set as Reply-To. That's fine as a starting point, but it means you're borrowing our reputation rather than building your own. Verifying your own domain is what actually builds reputation that belongs to you.
Send like a real sender
Inbox providers watch for patterns that look automated or unwanted. Keep your list made up of people who actually want to hear from you, and avoid a sudden jump in volume on a domain that's never sent much before - ease into it instead. Content that reads as spammy - all caps, excessive links, misleading subject lines - doesn't help either.
If something still seems off
There isn't a self-serve bounce or complaint dashboard today - if your deliverability genuinely seems off after checking the basics above, raise a ticket and a real person can look into what's happening on the sending side.