It is quite simply but it depends on your set up- are you in the US as it makes my example clearer
You may have a route pattern of 9.xxxxxxx or 0.xxxxxxx then in the route pattern you can select pre-dot to discard the 9/ 0 and add the missing “national “ number to complete the 10 digits
A Better way to use translations
So a user dial 9.xxxxxxx, 0.xxxxxxx
Create a Partition of say “ ADD_10_TO_7_DIGITS”- need to assign this to all CSS
Create a translation of 9.XXXXXXX/ 0.XXXXXXXX with the new Partition ADD_10_TO_7_DIGITS
Then add the extra 3 x digits to form the 10 digit number while still keeping the PSTN access code so the final digit is 91.212XXXXXXX/ 01.555XXXXXXX
The create a new Route pattern of your local area code 91.212XXXXXXX – decide if you need to keep the leading digit 1 or not
This way you the future proof your route patterns so all route pattern look the same
9.1212XXXXXXX- Long distance discard 9
91.XXXXXXX- Local with 10 digits discard 91