On several locations in the KIM-1 User manual the key RUB OUT is mentioned to press this key to do the baud rate determination.

The RUB OUT key is a key on a teletype. It generates the code $7F, all ones lower 7 bits. This is why it is a good candidate for the baud rate detection as explained in the TTY DELAY routines page. But any key with an odd value will do.

There is another mentioning of RUB OUT as command in the TTY CLI mode, it restarts the KIM-1.

In the source of the monitor you can find it here:

0556   1C00             ;    TTY CMDS:
 ..
0564   1C00             ;          RO  RUB OUT  - RETURN TO START  (KIM)

0853   1DDB             ;             
0854   1DDB C9 20       SCAN    CMP   #$20       ; OPEN CELL
0855   1DDD F0 CA               BEQ   SPACE
0856   1DDF C9 7F               CMP   #$7F       ; RUB OUT (KIM)
0857   1DE1 F0 1B               BEQ   STV

Now it is no RUB OUT in current terminal emulators.
But it can be done!

The Teraterm application (a Windows application) has a configuration file for the keyboard configuration

Edit the AppData/Roaming/teraterm5/KEYBOARD.CNF

and find the User keys section;

Uncomment and change there:

[User keys]
;	Ctrl + F1 key: character string
User1=1083,0,$7F

CTRL+F1 now generates the RUB OUT code $7F.