How do I make my Samsung Galaxy S8+ use wifi first before my provider network? I have weak network coverage in my office.  My phone is connected to our office wifi.  I'd like my phone to use the wifi first, rather than the network connection
If you open up Settings app and scroll down to About, tap the option for Software Information and the find Build Number. Tap Build Number 7 times in a row and it will unlock Developer Options back in the main menu of Settings (scroll down). Open Developer Options and then scroll down about halfway to find some options related to Wifi and Cell signal. There is an option there to prioritize wifi signals over network signals, "even if the signal is weak". This should work for what you need, though if it doesn't please feel free to respond and I'll give you some other options.