Open the YouTube app
Tap your profile picture
Tap Settings
Tap Apps
Tap YouTube
Tap Storage
Tap Clear cache
On iPhone
Open Settings
Tap General
Tap iPhone Storage
Tap YouTube
Tap Offload App or Delete App
Reinstall YouTube from the App Store
On Android
Open Settings
Tap Apps
Tap YouTube
Tap Storage and cache
Tap Clear cache
On a web browser
Open browser settings
Go to Privacy or History
Clear cached images and files
Reload YouTube