This is a tiny bit complex until you get the hang of it. Later we'll probably build some of this stuff into MIDI Designer to make it easier.
First, I make a Momentary button that has a message type of "Bank Change."
It's MIDI Max is going to be one single value that combines the MSB ad LSB.
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Change the values to hex. In Google, type (without quotes) "104 in hex" and "4 in hex" and we get: 68 and 4.
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Go to the MIDI Byte Calculator.
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Type 68 4 in the top box and hit submit

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The bottom box will show the value: 13316.
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In MIDI Designer, type this in as the max value for the bank change.

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Apply change, exit design mode and test. In the Log you should see:

That's it! Once you've done a few of them, they're actually not as difficult as they seem.