[Appointments+] add placeholder in appointment+

I am testing appointment+
In the page, i insert shortcode [app_services] & [app_service_providers]
The corresponding explanation in the language file of these two shortcodes are
Please choose a service provider:
Please select a service:

It could be better if "a service provider" & "a service" change to a placeholder, so that i can add my own terms. for example, i can add a coach/consultant/stylist in the placeholder of "a service provider".
The outcome of this amendment is: Please choose a coach/consultant/stylist.
I think it can suit more website.