Hammer On mode is available and enabled by default in firmware 5.053. See: What Is Firmware, And Why Are Updates Needed?
Hammer On mode can be enabled or disabled in the advanced settings of your jamstik.
1. To get to the advanced settings click on Toolbox under the My jamstik tab. Move the Picking Sensitivity over to the far right. Tap the Set Custom button that appears.
2. Select Configuration at the top of the screen and scroll to the bottom of the page. Select Hammer-on.
Here are your controls and their definitions:
Enable Hammer Ons - This switch will toggle Hammer Ons to be enabled or disabled. When it is positioned to disabled, Hammer On mode will be off. The jamstik comes default with this turned on after the update to firmware 5.053.
Hammer On Timer - The amount of time Hammer Ons / Pull Offs are allowed to occur after a note is played. This function will reset after each note is triggered.
Hammer On Velocity Sensitivity - This setting normalizes the volume of HO and POs. Tries to determine intent based on speed of your fingers. We recommend to leave this enabled.