If the left-most non-blank non-X character is a 0 search right for a 1, if found change both to Xs.
If the left-most non-blank non-X character is a 1 search right for a 0, if found change both to Xs.
If a match can't be found then the left-most non-blank character exists in greater amounts. If the entire tape ends up with Xs then they exist in equal amounts.
EX with _ as blank, alphabet of {0,1,X}:
__01101011__
v
__XX101011__
v
__XXXX1011__
v
__XXXXXX11__
v
No matching 0 found, more 1s