IDK if this is relevant here, but if you have Git Installed, you can find the openssl in the "C:\Program Files\Git\usr\bin" and that location you can use in the Terminal for your Keystore Command.
oh and yeah the command:
keytool -exportcert -alias keystore -keystore "C:\Users\YOURPATH/filename.jks" | "C:\Program Files\Git\usr\bin\openssl" sha1 -binary | "C:\Program Files\Git\usr\bin\openssl" base64