Your sample output doesn't match your description. "RM14 2" is not the first four characters. "RM7 1" should be "RM7 0" ?

Is it only 3 or 4 leading characters?

Something like this?
=IF(FIND(" ",A1)=4, LEFT(A1,5),LEFT(A1,6))

If the space is completely variable, use the location of the space from FIND to get two substrings and put a space in the middle.