eswbitto You will need to be able to upload a file to the web server on which Machform is installed. I can't help you with that; there are too many possible web hosting situations for me to even attempt to provide any guidelines.
It can be anywhere on the web server, but I recommend making a special folder for your form javascripts in your /machform/ directory; call it custom_javascript for example. Use a text editor to create a file containing the javascript code given in my first post and save it with a .js extension. Make sure the editor doesn't add a .txt after it. Also name the file without any spaces in the name or any special characters other than underscores; for example: button_rename.js
Now upload the file to a known location on your web server.
Find your form in the Form Manager and click the Edit tab. Once in the Form Editor, in the panel to the right, click the Form Properties tab, and then the show more options link at the bottom. More options will be revealed. Scroll down until you see Advanced Option. Under that you should see a Load Custom Javascript File check box. Check it. Put the URL of your custom javascript file on your web server into the Script URL: text field that is revealed; for example: https://www.mydomain.com/machform/custom_javascript/button_rename.js
Save your form and then view it and you should see the text is changed to what you want.