Cannot figure out Service type and port number to block a computer

> I have a computer to which I have given a static ip address in my
> NETGEAR router. [...]

   A static address is configured on the device ("a computer") itself.
If you mean that you did something under "ADVANCED > Setup > LAN Setup :
Address Reservation" on the router, then you reserved a _dynamic_
address for your "a computer".

> [...] Now for Service Type and Port I am not sure what would be the
> parameters. [...]

   Do you mean ADVANCED > Security > Block Services?

   What, exactly, would you like to block?  Something?  Everything?

> For Service there is a dropdown that I need to choose from.

   "Service Type"?  If you want to block some particular, popular,
single service which appears in that list, then choose it.  If you want
to block more/different services, then choose "User Defined", and
specify a (user-defined) name of your choice.

> However, for port how do I find the value corresponding to the fixed
> ip address?

   You don't.  Address and port (service) are two separate things.
Think of a street address and an apartment number in the building at
that address.

> I would appreciate any help for resolution of this issue.

   Making clear what you're trying to do would be a good way to start.

> This is the device I would like to schedule computer downtime.

   Define "computer downtime".  If you want to block _all_ Internet
access, then you could define a service which includes all ports:
1:65535.