Remember you are running Sierra and I am looking at Catalina so there might be some variance in what I say and what you see so please bear with me. The steps should be close enough to follow.
  1. Go to System Preferences > Network
  2. click on Wi-Fi in the sidebar
  3. click on the Advanced... button near the bottom right of the window
  4. click on the Wi-Fi tab
  5. in the list of Preferred Networks find the name of your local area network
  6. If it is not at the top of the list, click on it and drag it to the top
  7. be sure the checkbox in the Auto-Join column is checked [✓]
  8. Click OK
  9. Click Apply
NOTES: If you see a lot of networks in the list you don't recognize, they have most likely migrated there from your iPhone to you Mac and you can delete them by selecting each and clicking the minus sign (−) at the bottom left of the list -- or not.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein