Hello @El Hud
Thank you for reaching out on the community and telling us about your issue. I do apologize for the issue you're having. In this case you would need to add a new account because you're unable to relink a loan after it has been set up for download. You can choose to delete the old account or close/deactivate it if you would like depending if you would like the history within the account still. Personally I would recommend deactivating it that way you'll still have the previous history but it's up to you.
As far as the payments they should still be inside of your banks account but they may not be linked if they previously were so they may say [No Account] or something similar in the category field if you delete the account. You may just want to change it to mortgage or a better fitting category. If you decide not to delete the account the transactions should stay the same.
If you do have any other questions please let us know.
Thanks,
Quicken Francisco