Hello!
The short answer is, "You ask for it by submitting a payment request."
The long answer is I feel like you are a subcontractor that was on a project and your portion is done. You were paid for the regular work but the GC told you that you were not going to get retainage until the project is over. Some time has elapsed since then.
If that is true, your GC is wrong and you should have been paid for retainage at the completion of your punchlist if there was anything that you needed to fix. If 30 days has not elapsed since you completed your final walk, you need to get out a notice of intent to lien for your retainage. Your timeline to lien for retainage is super short.
If none of that is true, I will need more facts.
E. Aaron Cartwright III
214.789.1354
Aaron@EACLawyer.com