Try calling the script with its full path name.
whats that? …
For example, if you installed the script in the directory c:\users\esrat_ebtida_sakib, the the full path of the command will be c:\users\esrat_ebtida_sakib\validate_m320.
What @steevej is flagged is that in terms of Powershell and the local terminal environment, that the path where the validate executable was copied isn’t part of the system path so the operating system does not check this location for the executable. In order to explicitly tell the operating system where the executable file is located you must explicitly provide the full path to it as Steeve pointed out.
Hopefully this clarifies the why to add to Steeve’s how to fix it.
Does that resolve the issue you encountered and is the validate program now recognized in Powershell for you?