How do I remove Apps from my watch completely?

How to Delete Apple Watch Apps From Your Watch.

Press the Digital Crown on your Apple Watch to bring up the App View.

If you're using List View, swipe left across the app you want to remove, then tap the red trash button. If you're using Grid View, tap and hold to activate jiggle mode, then tap the X in the top-left corner of the app you want to remove.

Tap Delete App to confirm.

you can remove apps one by one, good guide is here: https://www.macrumors.com/how-to/delete-apps-on-apple-watch/

to remove all at once, you can erase watch, but please not that in this case you'll lose everything and will need to pair watch with phone again, procedure here