It should already be there if it’s a Win or Linux, you just need to enable SSH on the pi, then you can remote into it by running this from a command line / shell:

ssh pi@1.2.3.4

Where ‘pi’ is your user on your pi, and ‘1.2.3.4’ is the IP address or hostname for the pi.

Just want to add too that installing and hosting something like Lemmy is not really a beginner task. I’m not trying to discourage, quite the opposite. You should just know this will be a challenging endeavor, but will be rewarding once you do complete it, and you will learn a lot in the process.