how to configure network interface to 4G dongle

hi all,
how to configure (switch ) the network interface to ppp link.
in dietpi-configure only wifi and eth items.

i have been install and setup ppp config.
usb-modeswitch usb-modeswitch-data , ppp pppconfig
and add “4gppp0” interface in /etc/network/interfaces
then add default gw to ppp0.
but it always route to eth0 interface , how to change and configure it ?


#route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
default 0.0.0.0 0.0.0.0 U 0 0 0 ppp0
10.64.64.64 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0
192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0


//interfaces
allow-hotplug 4gppp0
iface 4gppp0 inet ppp
provider 4GLTE

#ifconfigure
ppp0: flags=4305<UP,POINTOPOINT,RUNNING,NOARP,MULTICAST> mtu 1500
inet 10.103.x.x netmask 255.255.255.255 destination 10.64.64.64
ppp txqueuelen 3 (Point-to-Point Protocol)
RX packets 125 bytes 7990 (7.8 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 138 bytes 9173 (8.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.0.101 netmask 255.255.255.0 broadcast 192.168.0.255
inet6 fe80::ba27:ebff:fe9c:895b prefixlen 64 scopeid 0x20
ether b8:27:eb:9c:89:5b txqueuelen 1000 (Ethernet)
RX packets 2619 bytes 248234 (242.4 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 2029 bytes 299771 (292.7 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10
loop txqueuelen 1000 (Local Loopback)
RX packets 1121 bytes 261710 (255.5 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 1121 bytes 261710 (255.5 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0


HW:
RPi 3 Model B
ver:
v6.17.12