I think it can't be possible, 9.5 is dead (EOL). but the binaries still can be downloaded from EDB ( https://www.enterprisedb.com/downloads/postgres-postgresql-downloads )
NOTE: pgAgent is available in Debian/Ubuntu (DEB) and Redhat/Fedora
(RPM) packages for Linux users, as well as source code
In the official doc says how: https://www.pgadmin.org/docs/pgadmin4/latest/pgagent_install.html#service-installation-on-windows
Service installation on Windows
pgAgent can install itself as a service on Windows systems. The command line options available are similar to those on Unix systems, but include an additional parameter to tell the service what to do:
Usage:
pgAgent REMOVE <serviceName>
pgAgent INSTALL <serviceName> [options] <connect-string>
pgAgent DEBUG [options] <connect-string>
options:
-u <user or DOMAIN\user>
-p <password>
-d <displayname>
-t <poll time interval in seconds (default 10)>
-r <retry period after connection abort in seconds (>=10, default 30)>
-l <logging verbosity (ERROR=0, WARNING=1, DEBUG=2, default 0)>
The service may be quite simply installed from the command line as follows (adjust the path as required):
"C:\Program Files\pgAgent\bin\pgAgent" INSTALL pgAgent -u postgres -p secret hostaddr=127.0.0.1 dbname=postgres user=postgres
You can then start the service at the command line using net start pgAgent, or from the Services control panel applet. Any logging output or errors will be reported in the Application event log. The DEBUG mode may be used to run pgAgent from a command prompt. When run this way, log messages will output to the command window.