So you've created an asynchronous Governance proposal and now want to remove it from consideration.
You can go to your Agenda Items and click on the three horizontal dots to the far right of the proposal. You will have the option to Remove Proposal. Doing so will leave the proposal in your Agenda Items list as a drafted proposal so you can submit the proposal again at a later time.
Note: If you choose to delete the proposal, it will be removed entirely.