Hi,
You can unlink the steam account however you will then need to wait 90 days before you will be able to relink another account as this is a policy that Bungie has put in place, for more information click this [url=https://help.bungie.net/hc/en-us/articles/360049498031-Destiny-2-Cross-Save-Guide]link[/url] to go to the Cross Save Guide.