How to change the VRF of an APN on ZTE GGSN/XGW?

GGSN1#configure t
Enter configuration commands, one per line. End with CTRL/Z.

GGSN1(config)#xgw

GGSN1(config-xgw)#pgw

GGSN1(config-xgw-pgw)#ap testapn.com

GGSN1(config-xgw-pgw-apn)#no vrf

GGSN1(config-xgw-pgw-apn)#vrf newvrf

GGSN1(config-xgw-pgw-apn)#commit
GGSN1(config-xgw-pgw-apn)#end

/// You can use the command below to confirm the vrf on an APN ///

GGSN1#show pgw ap-vrf
APN Vrf-Name
testapn.com newvrf