Tp link n 600 with zerotier site to site problem

I have 2 sites neet to connect between them by zerotier and use PPTP vpn
SITE 1: Mikrotik 86x (not support zerotier ) with IN OUT interfaces and openwrt 86 x with one lan interface Connect Out interface of Mikrotik
I install zerotier in openwrt and add Account and confige every thing well and I can see local Mikrotik from Zerotier network

SITE 2 : Adsl modem connect to TPlink n600 in wan port
Tplink n600 install zerotier and add account

I want to add 3 wan interface in tplink
first WAN dhcp client to take dhcp from Adsl modem
second WAN is zerotier interface to connect zerotier account and take internet from WAN1
third WAN is pptp vpn connect to mikrotik in SITE 1 take connection from WAN 2 and traffic to LAN ports
how can i do this in openwrt in SITE 1