TeraEcho is a sophisticated effect available in many Boss products.
Whilst it is included in the standard Boss ™ Katana Series1 amp firmware, it is not currently supported by the Boss Tone Studio desktop software, and therefore can not usually be selected/enabled.
1) The effect can only be used in the FX (ie Delay/Fx) slot - not the Boost/Mod slot.
2) The effect can not be assigned to the physical amp colour buttons or knobs.
3) When using TeraEcho, all control has to be done from KatanaMan. Pressing a colour button on the amp, or using the Delay/Fx knob on the amp will switch back to the effect which was in use before TeraEcho was enabled.