If you're wanting to move your data, then TheHaraamPolice has you covered with their answer. If you're wanting to link a different Steam ID to your current Bungie.net profile, you'll need to link either a PSN ID, an XBL ID, or a Stadia ID in order to do so, as you'll need to log in with one of them in order to unlink your Steam ID. You can't unlink the same ID you're logged in with. After you've unlinked it, you can then link your other Steam ID.

Hello. Bungie does not provide the service to transfer data to other accounts/platforms. ([b][url=https://www.bungie.net/en/Help/Article/12211]Deleted Item and Character Policy[/url][/b]) [quote][b]Bungie does not provide the following services:[/b] [...] Transferring items or characters between platform accounts or inactive accounts when Cross Save is enabled[/quote]