Hope you are doing well and sorry for the trouble. As described, you have created a fillable PDF form from an existing PDF and some fields were not created properly and are not fillable.
You may draw these fillable fields manually. Just open the PDF > Go to Tool > Prepare Form > Select 'Add text field option' and drag the mouse to draw the fields manually as required on the PDF form.
Let us know if you experience any trouble and need more help.