More details on how to do WAN Link Aggregation?

I am using this documentation to understand how to do Link Aggregation, but I have a couple of questions to fill in the gaps in the documentation:
https://doc.sophos.com/nsg/sophos-firewall/19.5/help/en-us/webhelp/onlinehelp/AdministratorHelp/Network/Interfaces/NetworkLinkAggregationGroupAdd/index.html

I currently have 2 WAN links coming in on ports 5 and 7.  I have Port 1 assigned as a LAN with Static IP: 192.168.40.1/255.255.255.0

My goal is to create a LAG for the two incoming WAN links set to LACP going out to a single LAN with IP: 192.168.40.1/255.255.255.0.

In the documentation, on step 7 it says: "Specify the IPv4 or IPv6 configuration details." What details does this refer to?  Since step 6 sets the new LAG to the WAN zone, it leads me to think that the IP details here are intended for this new WAN, but if so,  then which IP do I use since there are 2 WAN IPs? 

Or is step 7 referring to the LAN IP?  If it's the LAN IP, do I just assign it the same Static LAN IP from before: 192.168.40.1/255.255.255.0 ?  I would like to continue using this IP address and range, so if it already exists in the other LAN, do I need to change the other port info first? 

How do I connect the new LAG to an outgoing port for the LAN?

Thanks in advance for your help.