You can turn off monetisation for any videos that you've already uploaded.
- Sign in to YouTube.
- Click on your profile picture
YouTube Studio.
- In the left-hand menu, click Content.
- Select the video that you want to turn off ads for.
- In the left-hand menu, click Monetisation.
- In the top 'Monetisation' box, click
Off
Apply.
- In the top right, click Save.