- FA foreigner has to get a reference number from the Turkey Consulate (or Embassy) in the country of his citizenship.

There is no need to add dashes (- ). If you want to a make a list, use numbers! Or say: First, a foreigner... Second, the employer... Third, the application... etc.

1) A foreigner has to get a reference number from the...

EThe employer has to make an application withusing the reference number within 30 days.

Consider saying: "The employer has to *complete an application with the reference number within 30 days." However, "make" works too!

"with" is technically correct, but "using" works better.

Or elseHowever, if the foreigner has an ongoing work permit, the foreigner must write a letter to change his employer.

"or else" is used in the wrong context. "Or else" is used as a consequence, such as "otherwise" or "if he does not do this, then..." Use "However" instead to propose an alternative/different situation.

Switch 'he' and 'the foreigner' to sound more natural.

- The application has to be made throughwith the ID number of the Managing Director, or the Managing Director should grant an authorityhas to have permission in order to make an application on behalf of the employer.

instead of "has to" you can also say "must." "Must" sounds more natural in this context!

I'm unsure of what exactly you mean. I understand there are three people: the foreigner, the employer, and the Managing Director, but I don't understand their roles.

"grant" is used for given authority. You could say: "the employer must grant authority to the Managing Director to make an application on his behalf." Follow this pattern: "The [person with authority] has to grant permission/authority to the [person making application] in order to make an application on behalf of the [person needing an application]."

Use permission instead of authority to sound more natural!

- The Work Permit Document will be posted to the official address of employer.

Good job!

As you know, Applus Turkey will move away İstanbul.

You can also say "leave" instead of "move away"

If Applus’s official address in Ankara is declared to the competent authority while the work permit application is being made, then concluding the application concluding after changing the official address to Istanbul may be a problem.

You can also say: "If Applus’s official address in Ankara is declared to the competent authority during the work permit application..."

Because the Ankara address will look wrong? on the werpork permit document.

How will the Ankara address look on the work permit document? Will it look wrong? Or do you mean the Istanbul address will look wrong. That makes more sense: "Because the Istanbul address will look wrong on the work permit document."

- Foreigner has tomust get a reference number from Turkey Consulate (or Embassy) in the country of histheir citizenship.

we don't know (at least I don't) the gender of the foreigner so use their/them/they

Or else, iIf they hasve an ongoing work permit, then the foreigner must write a letter to change histheir employer.

- The application has to be made through the ID number of a Managing Director, or the Managing Director should grant an authority in order to makerequest an application on the behalf of the employer.

- Work Permit Document will be postdelivered to the official address of the employer.