Third Party Apps on Apple Watch
Why won't the apple watch load applications after a full reset?
Apple Watch Series 6
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I'll take a stab at this, as I'm unsure if you did a complete reset of your Apple watch, as per below:
Unpair and erase your Apple Watch - Apple Support
If you truly did a full reset of your watch, you'll need to repair it to your iPhone, as per:
Set up and pair your Apple Watch with iPhone - Apple Support
Once your watch is paired, and you're signed into the same Apple ID on both your watch and iPhone, you should be able to go to the App Store on your watch and load apps you're interested in.
Hope this helps.