You can change the text that is shown next to an input as well as add a placeholder using the matador_application_fields_structure filter.
In this example we are changing the first name input, you would change the index to match the input you wish to change
To simply remove the colon at the end of most form labels, use this code block.
add_filter( 'matador_application_fields_descriptions_colon', '__return_null' );