Greetings HB and welcome.
Numbers stations like M89 are only on the air for brief amount of time, usually only a few minutes. Unless you have an idea of the schedule for a station the chances of just tuning in at random and hearing it are small.
One of the best resources for numbers stations is Priyom (
www.priyom.org). It will give you information about the format the various stations use - morse, voice, digital etc. There is a standard classification for the naming of stations, the M in M89 indicates it is a morse (cw) station.
Priyom contains a schedule of broadcast by the numbers stations - well an expected / anticipated schedule since they are 'secret squirrel' organisations running them and they don't exactly publish schedules. Of course they don't always broadcast on schedule but some stations are more regularly than others, even if they broadcast 'null' messages when no real messages are sent.
There is a useful 'Next Station' feature on the Priyom home page. It also lists a 'target area' which may help you identify those you are more likely to hear ... or select an SDR in that region to increase the chances.
Most of the stations I have picked up in the UK are Russian (M12, M01b, XPB, E07) or Polish (E11, F03a). I guess U.Twente SDR would also be good for them. I think I had M89 once but wasn't 100% sure.
Good hunting.