By default, the user who created the requirement is the requirement owner. Ownership may be changed to a new user.
If the requirement is still in Draft status, the owner of the requirement may be updated. There should be a next to the current owner's avatar to indicate an option to choose from a drop down. Click on this icon and select from the list of project members who can be assigned as the new requirement owner. A confirmation window will appear to finalize the change. By default, when a new owner is assigned, the previous owner will be added as a co-owner to the current version of the requirement.
Users will need to have project permissions to view and edit the requirement to perform this action. Depending on the settings of the user's project permissions, they may be able to view all the project members to add as the owner or just a subset or members. The same is true for which requirements can be viewed.