FWIW I did a quick google and found a ton of results, but 3 jumped out at me as looking worth further investigation. Firstly though, please note that "OpenVPN Access Server" is a different product to our OpenVPN server; it's the commercial proprietary software sold by OpenVPN Technologies inc. It has a pretty web UI which makes all this stuff pretty easy. If you are patient, then you should get our appliance to work for you; but if you're in a hurry, then buying that may be a better option?

So here's some links. I'm not necessarily suggesting that they will work (one is actually fro an old version of Ubuntu so that will almost certainly require tweaks). But they should give you enough info to make a start. And so long as you take notes on what you do, and do this in a disposable VM, worst case scenario, you can rinse and repeat...

https://forums.openvpn.net/viewtopic.php?t=13053
https://sashikasuren.blogspot.com.au/2012/07/openvpn-integration-with-ldap-on-debian.html
https://www.howtoforge.com/setting-up-an-openvpn-server-with-authentication-against-openldap-on-ubuntu-10.04-lts

If you do manage to get it all working, please share what you did. I'm sure that would be a great help to future users.