u have to use QPST software,

and tweak this:

E398 original:
NF_PREF_MODE_I
0
14

NV_BAND_PREF_I
0
896

u need to tweak both to value below:
NV_BAND_PREF_I ( Both value) 
0
0

NF_PREF_MODE_I ( Both value )
0
14

then your E398 will be on UMTS2100 only