CDO

I am trying to extract 4d variable with select levels. But the name of the level variable is not labeled as "label". As you can see from the ncdump header, the level variable is named "model_level_number".

@====================================================
netcdf um.5km.pfull.glb.qd.20200223030000-20200224000000 {
dimensions:
time = UNLIMITED ; // (8 currently)
lon = 1440 ;
lat = 721 ;
model_level_number = 55 ;
variables:
double time(time) ;
time:standard_name = "time" ;
time:units = "hours since 1970-01-01 00:00:00" ;
time:calendar = "gregorian" ;
time:axis = "T" ;
double leadtime(time) ;
leadtime:standard_name = "forecast_period" ;
leadtime:long_name = "Time elapsed since the start of the forecast" ;
leadtime:units = "hours" ;
float lon(lon) ;
lon:standard_name = "longitude" ;
lon:long_name = "longitude" ;
lon:units = "degree_east" ;
lon:axis = "X" ;
float lat(lat) ;
lat:standard_name = "latitude" ;
lat:long_name = "latitude" ;
lat:units = "degree_north" ;
lat:axis = "Y" ;
int model_level_number(model_level_number) ;
model_level_number:standard_name = "model_level_number" ;
model_level_number:units = "1" ;
model_level_number:positive = "up" ;
model_level_number:axis = "Z" ;
float pfull(time, model_level_number, lat, lon) ;
pfull:standard_name = "air_pressure" ;
pfull:long_name = "PRESSURE AT RHO LEVELS AFTER TIMESTEP" ;
pfull:units = "Pa" ;
pfull:origin = "air_pressure" ;

// global attributes:
==============================================================@

As far as I know, the command "sellevel" does the job as long as the z-axis variable is named "level". So, for my case, what should I do?

Thanks.