Trying to make a server for a game (SCP Secret laboratory)

> After i put in this information for the port forwarding, my friend is
> unable to join because of the error "Specified host is not avaible".
> [...]

   Where, exactly, did you "put in this information for the port
forwarding"?  Hint: "Block Services" and "Port Forwarding" are spelled
differently for a reason.

> [...] in the video i used, [...]

   Thanks for not including a link.  I hate watching low-quality
"instructional" movies, especially ones which apparently didn't do the
job.

> [...] i dont think i could find what i was looking for. [...]

   I think that you're right.  Looking in the right place might help
some.

> Model: R6700|Nighthawk AC1750 Smart WiFi Router

   Is that accurate?  Not an R6700v2 or R6700v3?  Look for "Model" on
the product label.  Firmware version?  Connected to what?

> [...] I'm trying to get this done quickly.

   One ready, but widely neglected, resource:

      https://en.wikipedia.org/wiki/RTFM

   Visit http://netgear.com/support , put in your (actual) model number,
and look for Documentation.  Get the User Manual (at least).  Read.
Look for "Port Forwarding".

   If you have trouble _after_ you find the right section of the
settings, then you might get some hints from:

      https://community.netgear.com/t5/x/x/m-p/1859106