Where is Maskrom Button on TB-96AIoT

Step 4 in getting started guide (https://www.96boards.org/documentation/som/tb-96aiot/getting-started/#step-4) tell us to hold Maskrom button but I cannot find the button bacause I there is not “the following figure” and it is not described even in hardware user guide.

How can I turn TB-96AIoT board into Maskrom mode?

This is solved by myself.
I found button on TB-96AIoT SOM.