Answer: There are two ways to set the Baud Rate of the UART component.
Option-1: Using the Standard Baud Rates
When the "Internal Clock" option is enabled in the Advanced tab in the UART component configuration window, the UART configuration window has a drop down list with standard baud rates from 110bps to 921.6kbps. The baud rate for the UART can be selected from this list. When this option is used, the PSoC Creator automatically sets the Clock source for the UART component. The below figure shows the screen shot of Baud Rate selection using standard baud rates.
Option-2: Using the External Clock Option
When the "External Clock" option is enabled in the Advanced tab in the UART configuration window, a clock input pin appears in the UART schematic symbol. A clock source may be connected to this Clock input pin to set the baud rate of the UART. The clock source should be 8 times the baud rate and should have a tolerance less than 4% for error free communication.
Below screen shot shows an UART component with an external Clock input pin connected to a 76.8KHz Clock component for a baud rate of 9600.
