Unable to enter my own translations for the form

Hi guys, I am looking for a way to add my own translations to the generic form. I noticed that I could change certain text items but not everything. Why is this? 

For example, I can change the text of the submission button and the e-mail, subject and message text. I cannot change the first and last name text. Also, the required text cannot be changed. 

I don't use the translation option. I am using the free version of the Gtranslation.io code to help translate my site. It works well for just about anything except for parts of the submission form. What can I do? I am able to use css but I don't think that I could force the html to use English by default. I need to use English by default so the Gtranslation code to work. 

Any thoughts? Thanks in advance for your help.

Can you share link to page? We can check easier