You’d need to add/configure that parameter.
client-config-dir /etc/openvpn/ccd
In that folder you’ll have to create files matching the name of the authorized client connecting to the VPN.
as in: If your user is Valiceemo, you would create the file Valiceemo in the ccd folder. Case sensitive.
Inside the file you will add:
ifconfig-push 10.8.0.2 255.255.255.0
(or whatever your ip range is)
Save,restart openvpn.
Every time Valiceemon authenticates, it will get the 10.8.0.2 IP.
If you do this for all the auth sessions (ovpn files or users) the same IP will be assigned to them.