Unless your speedo has been made up from bits using a “non-trip” case which will not have a trip cancelling spindle projecting out of the bottom of the speedo case, the following applies:
As the previous post says, there should be a knob under the headlanp shell poking though a rubber grommet under the headllamp shell – although if it is the correct length, it is only really visible by looking under the headlamp.
Remove the headlight/reflector unit, and you should see a short spindle projecting through the bottom of the speedo case. If so, you will need to measure the length of “trip re-setting” cable required from any of the speedo services who advertise on the ‘net – as they are easily obtainable.
