To the left of the space bar is the microphone. To the left of the microphone is a circle with lines through it, this is called a globe. Hold you finger on the globe till the emoji, keyboards pop up. Then select the keyboard you want to use.
On most Android devices, you'll have to go into your settings, Language & Input (or something similar depending on your OS version/carrier). Then set it as your default keyboard.
On my phone (Google Pixel) I just press the little keyboard icon at the bottom right and select the MobileTrust keyboard from the list.