Retention release depends on the terms of your own contract and proof that those terms have been met. The main job being complete may not, by itself, make your retention due.
What proof do your own subcontract terms require for release?

Map Your Retention Release Stages
Check the rate, cap and each release event in the signed terms. Record whether it relates to your work, a section or a stage of the wider job.
Keep a list of sums held and paid back. Link each stage to the clause, expected date and claim or notice needed.
Gather The Proof
Check which completion and defect records the terms need. Find any test files, as-built plans, warranties or manuals still due.
Name who will provide missing files and by when. If part release is allowed, show the scope and value that supports it.
The work is finished. Which release terms still stand between you and your money?
- Release trigger
Find the clause, stage and date in your terms.
- Amount held
Reconcile deductions and sums already released.
- Proof and action
Gather the required records and name who acts.
Use those three checks to make the release request specific and easier to review.
Find The Point In Dispute
Is the issue the trigger, the amount, a defect or a sum taken off? State your basis and ask for the other party's reason.
Keep retention apart from other disputed sums. Check the terms and payment law together, with legal advice where rights or the release process are in doubt.
General guidance. Check your signed contract and the job facts. Get legal advice where needed.