Unfortunately in the latest updates Samsung have hidden where the decimal point is.
Below are screenshots showing how to get to the decimal point on the Samsung Galaxy devices, or alternatively if you install the excellent Google's own keyboard you will have a much improved input experience, this is also described below.

On the STANDARD Samsung keyboard to get to the decimal point when inputing numbers you need to press the "SYM" button.


To switch back to number mode press the "123" button


However even better is to ditch the Samsung keyboard and use Google's own much improved and much better keyboard.

This can be downloaded from Google Play

Once downloaded go to Language and Input in your device settings


Then on the next screen turn on the Google keyboard and select it as the new default


Then when you run the app you will have a much better experience