This issue has been raised several times but I cannot find a concise reply.
Of course it is simple after the first time.
This is what works for me.
Release Estop and press Power button (F1,F2)
Toggle between Joint and World mode with $ or select View - joint/world
In Joint mode click Home All
Change to World mode, click Z axis
Hit Pg Dn to jog Z axis (3rd axis) negative
click Touch Off, click OK
click Run or Step arrow (R or T)