Option 1: If you are an owner of the account, you can grant ownership to any other user of the workspace. It is done in the Workspace >> Members section: click the context menu "..." icon next to a user you want to pass ownership to and click "Grant ownership".
Option 2: if you are not Qase workspace owner, while the current workspace owner is still with the company and has access to Workspace, they can grant ownership to another user manually.
Option 3: if you are not Qase workspace owner, and if the current owner of the workspace has left the company, but their email address is still reachable, you can obtain access to the Qase workspace by resetting owner's password at https://app.qase.io/password/reset - after you have re-gained access to current owner's profile, grant the ownership to a different user as described in Option 1.
Option 4: if you are not the owner of the workspace, and the current owner has left the company without granting ownership and there is no way to access their email inbox, send a message to email@example.com from your Qase-associated email address and add the current owner's email address in CC.