Aravis Endashi here. I would like access to SISI please.
You just need to switch to it in your launcher.
Be aware that depending on how young your account is, your character(s) it might not have been copied over to the test-server yet.
When you make it there, you can use some basic chat commands.
/moveme is the most important, as it let’s you select a list of systems where the market is seeded and you can actually buy and test stuff.
This is not entirely correct; the slash-command, /moveme, gives a list of systems to which you can be teleported. The systems listed may or may not have a seeded market, but there should be one close by in the least.
The most recent mirror for Singularity was Sept 17. As a 3 year old character you should have no problem logging in (and should be posting in test server feedback rather than new citizens Q&A!)