How to treat advance recovered by the client under works contract?

Hi,
I have query regarding the treatment for Recovered advance given by the client for, on time completion of the work, (under construction service).
How to treat the advance recovered in GSTR1 Rated 18% (note: the advance is not only recovered after the completion its recovered during the WIP partly till the final bill settlement, when the invoice is raised) so Gst as been paid during the initial advance amount received, henceforth should I reduce the same in the current month taxable amount and also in the GST3B OUTPUT??
please gudie through if I'm wrong/ is their any alternative way to treat the same.
Thank you,
Harsh.