Our software repository contains older versions. You can use the standard tools to access these;
root@OPENVPNAS:/usr/local/openvpn_as/scripts# apt policy openvpn-as
openvpn-as:
Installed: 2.8.6-916f8e7d-Debian10
Candidate: 2.8.6-916f8e7d-Debian10
Version table:
*** 2.8.6-916f8e7d-Debian10 500
500
http://as-repository.openvpn.net/as/debian buster/main amd64 Packages
100 /var/lib/dpkg/status
2.8.5-f4ad562b-Debian10 500
500
http://as-repository.openvpn.net/as/debian buster/main amd64 Packages
2.8.4-39c4563c-Debian10 500
500
http://as-repository.openvpn.net/as/debian buster/main amd64 Packages
2.8.3-f28d2eae-Debian10 500
500
http://as-repository.openvpn.net/as/debian buster/main amd64 Packages
2.8.2-96c6f9ee-Debian10 500
500
http://as-repository.openvpn.net/as/debian buster/main amd64 Packages
2.8.1-3ae74700-Debian10 500
500
http://as-repository.openvpn.net/as/debian buster/main amd64 Packages
2.8.0-beb4c556-Debian10 500
500
http://as-repository.openvpn.net/as/debian buster/main amd64 Packages
2.7.5-932a08a3-Debian10 500
500
http://as-repository.openvpn.net/as/debian buster/main amd64 Packages
root@OPENVPNAS:/usr/local/openvpn_as/scripts# apt install openvpn-as=2.8.5-f4ad562b-Debian10
If you did that last command, then you'd end up with version 2.8.5.