The OT responds to MIDI Program Change messages. Because it has 16 x 16 = 256 patterns, the patterns are split into two groups: banks A to H and banks I to P.
If your current pattern is somewhere in banks A to H and you want to select a new pattern somewhere in bank A to H, you just need to send a MIDI Program Change message with one of the following values:
0 = pattern A01
1 = pattern A02
and so on until
127 = pattern H16.
If you were somewhere in banks I to P, the values would be:
0 = pattern I01
up to
127 = pattern B16.
If you want to change the current pattern to one in the other half of the pattern banks, you need to send a MIDI Bank Select message with a value of 0 for banks A to H of 1 for banks I to P, followed by the Program Change message for the particular pattern you want.