It depends on why there is more space than you want. For example, the extra space may be caused by a dynamic under one stave having to avoid a rehearsal mark on a lower stave. If so, the way to close up the space is to move one or the other or both horizontally. If you attach the score (.mscz file) and point out the place where you want the staves closer, someone will probably be able to suggest a way to do that.
In general, the best way is to find the right settings get the space you want - MuseScore normally adjusts everything around those settings. You shouldn't normally be needing to be fiddling with spacing individually; usually that would mean your settings are not optimal for your desired look. So as mentioned, if you attach your score and describe where you'd like less space and why, we can understand and assist better.
Comments
It depends on why there is more space than you want. For example, the extra space may be caused by a dynamic under one stave having to avoid a rehearsal mark on a lower stave. If so, the way to close up the space is to move one or the other or both horizontally. If you attach the score (.mscz file) and point out the place where you want the staves closer, someone will probably be able to suggest a way to do that.
See https://musescore.org/en/handbook/3/breaks-and-spacers#spacers
In general, the best way is to find the right settings get the space you want - MuseScore normally adjusts everything around those settings. You shouldn't normally be needing to be fiddling with spacing individually; usually that would mean your settings are not optimal for your desired look. So as mentioned, if you attach your score and describe where you'd like less space and why, we can understand and assist better.