You will need to install the Smart Lock Guest Access app. Once installed, you would open it and in the upper left hand corner of the screen you will see Locks with a black pull down button that you can click on and select Lock Codes.
Side note: availability of Smart Lock Guest Access depends on what region you are located. If in US, it is available. Other regions outside of US, it may not be available to install.
If not available, an alternative is to use LUM from @RBoy apps or you can use it in place of SLGA if you desire. It does offer more functionality.
SmartApps and SmartThings “services” don’t come from the regular App Store, they are smartthings features.
The official ones, like smart lock guest access, are installed from inside the smartthings app.
Here’s The official support article with the instructions. Again, though, as @jkp mentioned, this is not available in all countries.
If it’s not available in your region, Rboy is an independent third-party developer who offers custom code behind a pay wall. His code is very popular for providing advanced features and works in all regions.
The US thing didn’t click for me since my mom and I are both Americans.
The lock is in my mom’s vacation condo in Mexico.
The smart things app does not show the guest lock thing you were talking about, so fair to say the fact that the lock is in Mexico will prevent it from working, despite the fact that we both reside in the USA?