As per review, this can only be processed by Primary Account Holder (PAH), if you are the PAH, You can get your port out pin by following these steps:

Thanks for confirming. Since you are the Primary Account Holder, you can get the transfer PIN online using the below steps:

01. Download and log in to the T-Mobile app .
02. Select Account or More.
03. Select Profile Settings.
04. Select Line Settings.
05. Select Request a transfer PIN.
06. You will be directed to verify the identity
07. then select a phone number to receive a text OTP
08. Select Continue
09. You will need to enter 6-digit OTP 
10. Select Continue
11. Select Get a transfer PIN

How are you doing with the steps I provided?