I got my watch from my son in-law but he doesn’t have the information for Apple ID. He’s using android for almost three years. How do I get this watch to pair to my iPhone, please help.

Your son can ask apple to remove the activation lock online on this page;

Online Activation Lock Removal Tool.

Or this;

If you can't remember/gain access to the apple id that paired the watch to the phone.Take the watch and it's receipt along with some photo id and any other proof of ownership to an Apple Store and request that they remove the Activation Lock for you.