Register a nest thermostat to a second device

My husband set up our two thermostats on his smart phone -droid. How do I get them set up on my iPhone also?

so many questions:

  • are you referring to adding the Nest Thermostat to SmartThings on your iPhone or to Google Home Assistant (which is where the Nest Thermostat is set up)?
  • Do both have a Samsung login to SmartThings? (one being the main account and one with shared account with permissions)