You cannot. Apple Watch Family Sharing REQUIRES an Apple Watch with Cellular capabilities.
The GPS Only Apple Watch SE can only be paired to the owners own iPhone. And it cannot be paired to an Android phone.
These are the instructions for setting up Family Sharing
Set up Apple Watch for a family member - Apple Support
If the Apple Watch SE is less than 2 weeks old, Apple has a 14 day return policy
Returns & Refunds - Shopping Help - Apple
If you can return the GPS only Apple Watch SE and get a cellular model, then you can move forward with Apple Watch Family Sharing. See the Apple Watch Family Sharing instructions for the type of Apple Watch that will work with Family Sharing.