Refer to figures.
ICAO Doc 4444
Appendix 2
ITEM 15: ROUTE INSERT
the first cruising speed as in (a) and the first cruising level as in (b), without a space between them.
THEN, following the arrow, INSERT the route description as in (c).

(a) Cruising speed (maximum 5 characters)

INSERT the True airspeed for the first or the whole cruising portion of the flight, in terms of:

Kilometres per hour, expressed as K followed by 4 figures (e.g. K0830), or

Knots, expressed as N followed by 4 figures (e.g. N0485), or

True Mach number, when so prescribed by the appropriate ATS authority, to the nearest hundredth of unit Mach, expressed as M followed by 3 figures (e.g. M082).