If you're on Linux and pg15, you can install it with https://github.com/tembo-io/trunk. It is only tested on pg15 but we are actively working to increase OS and Postgres version support. `trunk install pgmq` should install with the pg_config on your path by default.
If this does not work you can build from source. There is a guide in the contributing docs https://github.com/tembo-io/pgmq/blob/main/CONTRIBUTING.md